System and method for manufacturing arthroplasty jigs having improved mating accuracy

ABSTRACT

Disclosed herein is a method of defining a mating surface in a first side of an arthroplasty jig. The mating surface is configured to matingly receive and contact a corresponding patient surface including at least one of a bone surface and a cartilage surface. The first side is oriented towards the patient surface when the mating surface matingly receives and contacts the patient surface. The method may include: a) identifying a contour line associated with the patient surface as represented in a medical image; b) evaluating via an algorithm the adequacy of the contour line for defining a portion of the mating surface associated with the contour line; c) modifying the contour line if the contour line is deemed inadequate; and d) employing the modified contour line to define the portion of the mating surface associated with the contour line.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 12/505,056, filed Jul. 17, 2009, which application claims thebenefit of priority under 35 USC §119(e) to U.S. Patent Application No.61/083,053 entitled “System and Method for Manufacturing ArthroplastyJigs Having Improved Mating Accuracy,” and filed Jul. 23, 2008. Eachapplication referenced above is hereby incorporated by reference in itsentirety as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to systems and methods for manufacturingcustomized arthroplasty cutting jigs. More specifically, the presentinvention relates to automated systems and methods manufacturing suchjigs.

BACKGROUND OF THE INVENTION

Over time and through repeated use, bones and joints can become damagedor worn. For example, repetitive strain on bones and joints (e.g.,through athletic activity), traumatic events, and certain diseases(e.g., arthritis) can cause cartilage in joint areas, which normallyprovides a cushioning effect, to wear down. When the cartilage wearsdown, fluid can accumulate in the joint areas, resulting in pain,stiffness, and decreased mobility.

Arthroplasty procedures can be used to repair damaged joints. During atypical arthroplasty procedure, an arthritic or otherwise dysfunctionaljoint can be remodeled or realigned, or an implant can be implanted intothe damaged region. Arthroplasty procedures may take place in any of anumber of different regions of the body, such as a knee, a hip, ashoulder, or an elbow.

One type of arthroplasty procedure is a total knee arthroplasty (“TKA”),in which a damaged knee joint is replaced with prosthetic implants. Theknee joint may have been damaged by, for example, arthritis (e.g.,severe osteoarthritis or degenerative arthritis), trauma, or a raredestructive joint disease. During a TKA procedure, a damaged portion inthe distal region of the femur may be removed and replaced with a metalshell, and a damaged portion in the proximal region of the tibia may beremoved and replaced with a channeled piece of plastic having a metalstem. In some TKA procedures, a plastic button may also be added underthe surface of the patella, depending on the condition of the patella.

Implants that are implanted into a damaged region may provide supportand structure to the damaged region, and may help to restore the damagedregion, thereby enhancing its functionality. Prior to implantation of animplant in a damaged region, the damaged region may be prepared toreceive the implant. For example, in a knee arthroplasty procedure, oneor more of the bones in the knee area, such as the femur and/or thetibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) toprovide one or more surfaces that can align with the implant and therebyaccommodate the implant.

Accuracy in implant alignment is an important factor to the success of aTKA procedure. A one- to two-millimeter translational misalignment, or aone- to two-degree rotational misalignment, may result in imbalancedligaments, and may thereby significantly affect the outcome of the TKAprocedure. For example, implant misalignment may result in intolerablepost-surgery pain, and also may prevent the patient from having full legextension and stable leg flexion.

To achieve accurate implant alignment, prior to treating (e.g., cutting,drilling, reaming, and/or resurfacing) any regions of a bone, it isimportant to correctly determine the location at which the treatmentwill take place and how the treatment will be oriented. In some methods,an arthroplasty jig may be used to accurately position and orient afinishing instrument, such as a cutting, drilling, reaming, orresurfacing instrument on the regions of the bone. The arthroplasty jigmay, for example, include one or more apertures and/or slots that areconfigured to accept such an instrument.

A system and method has been developed for producing customizedarthroplasty jigs configured to allow a surgeon to accurately andquickly perform an arthroplasty procedure that restores thepre-deterioration alignment of the joint, thereby improving the successrate of such procedures. Specifically, the customized arthroplasty jigsare indexed such that they matingly receive the regions of the bone tobe subjected to a treatment (e.g., cutting, drilling, reaming, and/orresurfacing). The customized arthroplasty jigs are also indexed toprovide the proper location and orientation of the treatment relative tothe regions of the bone. The indexing aspect of the customizedarthroplasty jigs allows the treatment of the bone regions to be donequickly and with a high degree of accuracy that will allow the implantsto restore the patient's joint to a generally pre-deteriorated state.However, the system and method for generating the customized jigs oftenrelies on a human to “eyeball” bone models on a computer screen todetermine configurations needed for the generation of the customizedjigs. This is “eyeballing” or manual manipulation of the bone modes onthe computer screen is inefficient and unnecessarily raises the time,manpower and costs associated with producing the customized arthroplastyjigs. Furthermore, a less manual approach may improve the accuracy ofthe resulting jigs.

There is a need in the art for a system and method for reducing thelabor associated with generating customized arthroplasty jigs. There isalso a need in the art for a system and method for increasing theaccuracy of customized arthroplasty jigs.

SUMMARY

Disclosed herein is a method of manufacturing an arthroplasty jig. Inone embodiment, the method includes: generating two-dimensional imagesof at least a portion of a bone forming a joint; generating a firstthree-dimensional computer model of the at least a portion of the bonefrom the two-dimensional images; generating a second three-dimensionalcomputer model of the at least a portion of the bone from thetwo-dimensional images; causing the first and second three-dimensionalcomputer models to have in common a reference position, wherein thereference position includes at least one of a location and anorientation relative to an origin; generating a first type of data withthe first three-dimensional computer model; generating a second type ofdata with the second three-dimensional computer model; employing thereference position to integrate the first and second types of data intoan integrated jig data; using the integrated jig data at a manufacturingdevice to manufacture the arthroplasty jig.

Disclosed herein is a method of manufacturing an arthroplasty jig. Inone embodiment, the method includes: generating two-dimensional imagesof at least a portion of a bone forming a joint; extending an open-loopcontour line along an arthroplasty target region in at least some of thetwo-dimensional images; generating a three-dimensional computer model ofthe arthroplasty target region from the open-loop contour lines;generating from the three-dimensional computer model surface contourdata pertaining to the arthroplasty target area; and using the surfacecontour data at a manufacturing machine to manufacture the arthroplastyjig.

Disclosed herein is a method of manufacturing an arthroplasty jig. Inone embodiment, the method includes: determining from an image at leastone dimension associated with a portion of a bone; comparing the atleast one dimension to dimensions of at least two candidate jig blanksizes; selecting the smallest of the jig blank sizes that issufficiently large to accommodate the at least one dimension; providinga jig blank of the selected size to a manufacturing machine; andmanufacturing the arthroplasty jig from the jig blank.

Disclosed herein are arthroplasty jigs manufactured according to any ofthe aforementioned methods of manufacture. In some embodiments, thearthroplasty jigs may be indexed to matingly receive arthroplasty targetregions of a joint bone. The arthroplasty jigs may also be indexed toorient saw cut slots and drill hole guides such that when thearthroplasty target regions are matingly received by the arthroplastyjig, the saw cuts and drill holes administered to the arthroplastytarget region via the saw cut slots and drill hole guides willfacilitate arthroplasty implants generally restoring the joint to apre-degenerated state (i.e., natural alignment state).

Disclosed herein is a method of computer generating a three-dimensionalsurface model of an arthroplasty target region of a bone forming ajoint. In one embodiment, the method includes: generatingtwo-dimensional images of at least a portion of the bone; generating anopen-loop contour line along the arthroplasty target region in at leastsome of the two-dimensional images; and generating the three-dimensionalmodel of the arthroplasty target region from the open-loop contourlines.

Disclosed herein is a method of generating a three-dimensionalarthroplasty jig computer model. In one embodiment, the method includes:comparing a dimension of at least a portion of a bone of a joint tocandidate jig blank sizes; and selecting from the candidate jig blanksizes a smallest jig blank size able to accommodate the dimensions ofthe at least a portion of the bone.

Disclosed herein is a method of generating a three-dimensionalarthroplasty jig computer model. In one embodiment, the method includes:forming an interior three-dimensional surface model representing anarthroplasty target region of at least a portion of a bone; forming anexterior three-dimensional surface model representing an exteriorsurface of a jig blank; and combining the interior surface model andexterior surface model to respectively form the interior surface andexterior surface of the three-dimensional arthroplasty jig computermodel.

Disclosed herein is a method of generating a production file associatedwith the manufacture of arthroplasty jigs. The method includes:generating first data associated a surface contour of an arthroplastytarget region of a joint bone; generating second data associated with atleast one of a saw cut and a drill hole to be administered to thearthroplasty target region during an arthroplasty procedure; andintegrating first and second data, wherein a positional relationship offirst data relative to an origin and a positional relationship of seconddata relative to the origin are coordinated with each other to begenerally identical during the respective generations of first andsecond data.

Disclosed herein is a method of defining a mating surface in a firstside of an arthroplasty jig. The mating surface is configured tomatingly receive and contact a corresponding patient surface includingat least one of a bone surface and a cartilage surface. The first sideis oriented towards the patient surface when the mating surface matinglyreceives and contacts the patient surface. In one embodiment, the methodincludes: a) identifying a contour line associated with the patientsurface as represented in a medical image; b) evaluating via analgorithm the adequacy of the contour line for defining a portion of themating surface associated with the contour line; c) modifying thecontour line if the contour line is deemed inadequate; and d) employingthe modified contour line to define the portion of the mating surfaceassociated with the contour line.

Disclosed herein is an arthroplasty jig for assisting in the performanceof an arthroplasty procedure associated with a patient surface includingat least one of a bone surface and a cartilage surface. In oneembodiment, the jig may include a first side, a second side generallyopposite the first side, and a mating surface in the first side andconfigured to matingly receive and contact at least a portion of thepatient surface. The first side may be configured to be oriented towardsthe patient surface when the mating surface matingly receives andcontacts the patient surface. The mating surface may be definedaccording to the following process steps: a) identifying a contour lineassociated with the patient surface as represented in a medical image;b) evaluating via an algorithm the adequacy of the contour line fordefining a portion of the mating surface associated with the contourline; c) modifying the contour line if the contour line is deemedinadequate; and d) employing the modified contour line to define theportion of the mating surface associated with the contour line.

Disclosed herein is a femoral arthroplasty jig for assisting in theperformance of a femoral arthroplasty procedure on a femoralarthroplasty target region. In one embodiment the jig includes a firstside, a second side generally opposite the first side; and a matingsurface in the first side and configured to matingly receive and contactcertain surfaces of the femoral arthroplasty target region. The certainsurfaces may bed limited to a medial articular condyle surface, alateral articular condyle surface, and a generally planar area of ananterior side of a femoral shaft. The first side may be configured to beoriented towards the femoral arthroplasty target region surface when themating surface matingly receives and contacts the certain surfaces.

Disclosed herein is a tibial arthroplasty jig for assisting in theperformance of a tibial arthroplasty procedure on a tibial arthroplastytarget region. In one embodiment, the jig includes a first side, asecond side generally opposite the first side, and a mating surface. Themating surface may be in the first side and configured to matinglyreceive and contact certain surfaces of the tibial arthroplasty targetregion. The certain surfaces may be limited to a medial articularplateau surface, a lateral articular plateau surface, and a generallyplanar area of an anterior side of a tibial shaft. The first side may beconfigured to be oriented towards the tibial arthroplasty target regionsurface when the mating surface matingly receives and contacts thecertain surfaces.

Disclosed herein is a tibial arthroplasty jig for assisting in theperformance of a tibial arthroplasty procedure on a tibial arthroplastytarget region. In one embodiment, the jig includes a first side, asecond side generally opposite the first side. The second side mayinclude a mating surface in the first side. The mating surface may beconfigured to matingly receive and contact a generally planar area of ananterior side of a tibial shaft distal of the tibial plateau edge andgenerally proximal of the tibial tuberosity. The first side may beconfigured to be oriented towards the tibial arthroplasty target regionsurface when the mating surface matingly receives and contacts theplanar area.

Disclosed herein is a femoral arthroplasty jig for assisting in theperformance of a femoral arthroplasty procedure on a femoralarthroplasty target region. In one embodiment, the jig includes a firstside, a second side generally opposite the first side, and a matingsurface in the first side. The mating surface may be configured tomatingly receive and contact a generally planar area of an anterior sideof a femoral shaft generally proximal of the patellar facet boarder andgenerally distal an articularis genu. The first side may be configuredto be oriented towards the femoral arthroplasty target region surfacewhen the mating surface matingly receives and contacts the planar area.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. As will be realized, theinvention is capable of modifications in various aspects, all withoutdeparting from the spirit and scope of the present invention.Accordingly, the drawings and detailed description are to be regarded asillustrative in nature and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a system for employing the automatedjig production method disclosed herein.

FIGS. 1B-1E are flow chart diagrams outlining the jig production methoddisclosed herein.

FIGS. 1F and 1G are, respectively, bottom and top perspective views ofan example customized arthroplasty femur jig.

FIGS. 1H and 1I are, respectively, bottom and top perspective views ofan example customized arthroplasty tibia jig.

FIG. 2A is an anterior-posterior image slice of the damaged lower orknee joint end of the patient's femur, wherein the image slice includesan open-loop contour line segment corresponding to the targeted regionof the damaged lower end.

FIG. 2B is a plurality of image slices with their respective open-loopcontour line segments, the open-loop contour line segments beingaccumulated to generate the 3D model of the targeted region.

FIG. 2C is a 3D model of the targeted region of the damaged lower end asgenerated using the open-loop contour line segments depicted in FIG. 2B.

FIG. 2D is an anterior-posterior image slice of the damaged lower orknee joint end of the patient's femur, wherein the image slice includesa closed-loop contour line corresponding to the femur lower end,including the targeted region.

FIG. 2E is a plurality of image slices with their respective closed-loopcontour line segments, the closed-loop contour lines being accumulatedto generate the 3D model of the femur lower end, including the targetedregion.

FIG. 2F is a 3D model of the femur lower end, including the targetedregion, as generated using the closed-loop contour lines depicted inFIG. 2B.

FIG. 2G is a flow chart illustrating an overview of the method ofproducing a femur jig.

FIG. 3A is a top perspective view of a left femoral cutting jig blankhaving predetermined dimensions.

FIG. 3B is a bottom perspective view of the jig blank depicted in FIG.3A.

FIG. 3C is plan view of an exterior side or portion of the jig blankdepicted in FIG. 3A.

FIG. 4A is a plurality of available sizes of left femur jig blanks, eachdepicted in the same view as shown in FIG. 3C.

FIG. 4B is a plurality of available sizes of right femur jig blanks,each depicted in the same view as shown in FIG. 3C.

FIG. 5 is an axial view of the 3D surface model or arthritic model ofthe patient's left femur as viewed in a direction extending distal toproximal.

FIG. 6 depicts the selected model jig blank of FIG. 3C superimposed onthe model femur lower end of FIG. 5.

FIG. 7A is an example scatter plot for selecting from a plurality ofcandidate jig blanks sizes a jig blank size appropriate for the lowerend of the patient's femur.

FIG. 7B is a flow diagram illustrating an embodiment of a process ofselecting an appropriately sized jig blank.

FIG. 8A is an exterior perspective view of a femur jig blank exteriorsurface model.

FIG. 8B is an interior perspective view of the femur jig blank exteriorsurface model of FIG. 8A.

FIG. 9A is a perspective view of the extracted jig blank exteriorsurface model being combined with the extracted femur surface model.

FIG. 9B is a perspective view of the extracted jig blank exteriorsurface model combined with the extracted femur surface model.

FIG. 9C is a cross section of the combined jig blank exterior surfacemodel and the femur surface model as taken along section line 9C-9C inFIG. 9B.

FIG. 10A is an exterior perspective view of the resulting femur jigmodel.

FIG. 10B is an interior perspective view of the femur jig model of FIG.10A.

FIG. 11 illustrates a perspective view of the integrated jig modelmating with the “arthritic model”.

FIG. 12A is an anterior-posterior image slice of the damaged upper orknee joint end of the patient's tibia, wherein the image slice includesan open-loop contour line segment corresponding to the target area ofthe damaged upper end.

FIG. 12B is a plurality of image slices with their respective open-loopcontour line segments, the open-loop contour line segments beingaccumulated to generate the 3D model of the target area.

FIG. 12C is a 3D model of the target area of the damaged upper end asgenerated using the open-loop contour line segments depicted in FIG.12B.

FIG. 13A is a top perspective view of a right tibia cutting jig blankhaving predetermined dimensions.

FIG. 13B is a bottom perspective view of the jig blank depicted in FIG.13A.

FIG. 13C is plan view of an exterior side or portion of the jig blankdepicted in FIG. 13A.

FIG. 14A is a plurality of available sizes of right tibia jig blanks,each depicted in the same view as shown in FIG. 13C.

FIG. 14B is a plurality of available sizes of left tibia jig blanks,each depicted in the same view as shown in FIG. 13C.

FIG. 15 is an axial view of the 3D surface model or arthritic model ofthe patient's right tibia as viewed in a direction extending proximal todistal.

FIG. 16 depicts the selected model jig blank of FIG. 13C superimposed onthe model tibia upper end of FIG. 15.

FIG. 17A is an example scatter plot for selecting from a plurality ofcandidate jig blanks sizes a jig blank size appropriate for the upperend of the patient's tibia.

FIG. 17B is a flow diagram illustrating an embodiment of a process ofselecting an appropriately sized jig blank.

FIG. 18A is an exterior perspective view of a tibia jig blank exteriorsurface model.

FIG. 18B is an interior perspective view of the tibia jig blank exteriorsurface model of FIG. 18A.

FIG. 19A is a perspective view of the extracted jig blank exteriorsurface model being combined with the extracted tibia surface model.

FIGS. 19B-19D are perspective views of the extracted jig blank exteriorsurface model combined with the extracted tibia surface model.

FIG. 20A is an exterior perspective view of the resulting tibia jigmodel.

FIG. 20B is an interior perspective view of the tibia jig model of FIG.20A.

FIG. 21 illustrates a perspective view of the integrated jig modelmating with the “arthritic model”.

FIG. 22A illustrates the distal axial view of the 3D model of thepatient's femur shown in FIG. 5 with the contour lines of the imageslices shown and spaced apart by the thickness D_(T) of the slices.

FIG. 22B represents a coronal view of a 3D model of the patient's femurwith the contour lines of the image slices shown and spaced apart by thethickness D_(T) of the slices.

FIG. 23 illustrates an example sagittal view of compiled contour linesof successive sagittal 2D MRI images based on the slices shown in FIGS.22A-B with a slice thickness D_(T) of 2 mm.

FIG. 24 illustrates an example contour line of one of the contour linesdepicted in FIGS. 22A-23, wherein the contour line is depicted in asagittal view and is associated with an image slice of the femoralcondyle.

FIG. 25 represents an example overestimation algorithm that may be usedto identify and adjust for irregular contour line regions when formingthe 3D model.

FIG. 26 depicts implementing an example analysis scheme (according toblock 2506) on the irregular contour line region 2402B of FIG. 24.

FIG. 27 depicts the irregular region 2402B from FIG. 26 including aproposed area of overestimation, wherein an overestimation procedurecreates an adjusted contour line and positionally deviates the adjustedcontour line from the original surface profile contour line.

FIG. 28 illustrates the example analysis scheme according to thealgorithm of FIG. 25 implemented on the irregular region 2402C from FIG.24 where an irregular surface of the condylar contour is observed.

FIG. 29A depicts the irregular region 2402C from FIG. 28 including aproposed area of overestimation indicated by the dashed line areas2902A-B.

FIG. 29B is similar to FIG. 29A, except depicting a tool with a largerdiameter.

FIG. 29C is similar to FIG. 29B, except depicting a tool with a largerdiameter.

FIG. 30 depicts the irregular region 2402D from FIG. 24 including aproposed area of overestimation indicated by the dashed line.

FIG. 31 shows an analysis of the regular region 2402A from FIG. 24.

FIG. 32A is a diagrammatic sagittal-coronal-distal isometric view ofthree contour lines of three adjacent image slices depicting angularrelationships that may be used to determine whether portions of the oneor more contour lines may be employed to generate 3D computer models.

FIGS. 32B-G are example right triangles that may be used for determiningthe angular deviation 8 between corresponding coordinate points ofcontour lines of adjacent image slices per block 2514 of FIG. 25.

FIG. 33A depicts portions of contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) in a sagittal view similar to that of FIG. 23.

FIG. 33B is a bone surface contour line and a linear interpolation bonesurface contour line as viewed along a section line 33B-33B transverseto image slices containing the contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) of FIG. 33A.

FIG. 33C depicts portions of contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) in a sagittal view similar to that of FIG. 23.

FIG. 33D is a bone surface contour line and a linear interpolation bonesurface contour line as viewed along a section line 33D-33D transverseto image slices containing the contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) of FIG. 33C.

FIG. 33E depicts portions of contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) in a sagittal view similar to that of FIG. 23.

FIG. 33F is a bone surface contour line and a linear interpolation bonesurface contour line as viewed along a section line 33F-33F transverseto image slices containing the contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) of FIG. 33E.

FIG. 34 is a distal view similar to that of FIG. 5 depicting contourlines produced by imaging the right femur at an image spacing D_(T) of,for example, 2 mm.

FIGS. 35-38 are sagittal views of the contour lines of respectiveregions of FIG. 34.

FIG. 39A is distal-sagittal isometric view of a femoral distal end.

FIG. 39B is a bottom perspective view of an example customizedarthroplasty femur jig that has been generated via the overestimationprocess disclosed herein.

FIG. 39C is an anterior-posterior cross-section of the femur jig of FIG.39B mounted on the femur distal end of FIG. 39A.

FIG. 39D is a coronal view of the anterior side of the femoral distalend.

FIG. 40 depicts closed-loop contour lines that are image segmented fromimage slices, wherein the contour lines outline the cortical bonesurface of the lower end of the femur.

FIG. 41A illustrates the proximal axial view of the 3D model of thepatient's tibia shown in FIG. 15 with the contour lines of the imageslices shown and spaced apart by the thickness D_(T) of the slices.

FIG. 41B represents a coronal view of a 3D model of the patient's tibiawith the contour lines of the image slices shown and spaced apart by thethickness D_(T) of the slices.

FIG. 42 illustrates an example sagittal view of compiled contour linesof successive sagittal 2D MRI images based on the slices shown in FIGS.41A-B with a slice thickness D_(T) of 2 mm.

FIG. 43 illustrates an example contour line of one of the contour linesdepicted in FIGS. 41A-42, wherein the contour line is depicted in asagittal view and is associated with an image slice of the tibiaplateau.

FIG. 44 depicts implementing an example analysis scheme (according toblock 2506) on the irregular contour line region 4302B of FIG. 43.

FIG. 45 depicts the irregular region 4302B from FIG. 44 including aproposed area of overestimation, wherein an overestimation procedurecreates an adjusted contour line and positionally deviates the adjustedcontour line from the original surface profile contour line.

FIGS. 46A and 46B show an analysis of the regular regions 4302A and4302C from FIG. 43.

FIG. 47 is a distal view similar to that of FIG. 15 depicting contourlines produced by imaging the left tibia at an image spacing D_(T) of,for example, 2 mm.

FIGS. 48-51 are sagittal views of the contour lines of respectiveregions of FIG. 47.

FIG. 52A is distal-sagittal isometric view of a tibial proximal end.

FIGS. 52B-C are, respectively, top and bottom perspective views of anexample customized arthroplasty tibia jig that has been generated viathe overestimation process disclosed herein.

FIG. 52D is an anterior-posterior cross-section of the tibia jig ofFIGS. 52B-C mounted on the tibia proximal end of FIG. 52A.

FIG. 52E is a coronal view of the anterior side of the tibial proximalend.

FIG. 53 depicts closed-loop contour lines that are image segmented fromimage slices, wherein the contour lines outline the cortical bonesurface of the upper end of the tibia.

FIG. 54 is an anterior isometric view of the femur distal end.

FIG. 55 is an anterior isometric view of the tibia proximal end.

DETAILED DESCRIPTION

Disclosed herein are customized arthroplasty jigs 2 and systems 4 for,and methods of, producing such jigs 2. The jigs 2 are customized to fitspecific bone surfaces of specific patients. Depending on the embodimentand to a greater or lesser extent, the jigs 2 are automatically plannedand generated and may be similar to those disclosed in these three U.S.patent application Ser. No. 11/656,323 to Park et al., titled“Arthroplasty Devices and Related Methods” and filed Jan. 19, 2007; U.S.patent application Ser. No. 10/146,862 to Park et al., titled “ImprovedTotal Joint Arthroplasty System” and filed May 15, 2002; and U.S. patentSer. No. 11/642,385 to Park et al., titled “Arthroplasty Devices andRelated Methods” and filed Dec. 19, 2006. The disclosures of these threeU.S. patent applications are incorporated by reference in theirentireties into this Detailed Description.

a. Overview of System and Method for Manufacturing CustomizedArthroplasty Cutting Jigs

For an overview discussion of the systems 4 for, and methods of,producing the customized arthroplasty jigs 2, reference is made to FIGS.1A-1E. FIG. 1A is a schematic diagram of a system 4 for employing theautomated jig production method disclosed herein. FIGS. 1B-1E are flowchart diagrams outlining the jig production method disclosed herein. Thefollowing overview discussion can be broken down into three sections.

The first section, which is discussed with respect to FIG. 1A and[blocks 100-125] of FIGS. 1B-1E, pertains to an example method ofdetermining, in a three-dimensional (“3D”) computer model environment,saw cut and drill hole locations 30, 32 relative to 3D computer modelsthat are termed restored bone models 28. The resulting “saw cut anddrill hole data” 44 is referenced to the restored bone models 28 toprovide saw cuts and drill holes that will allow arthroplasty implantsto restore the patient's joint to its pre-degenerated state or, in otherwords, its natural alignment state.

The second section, which is discussed with respect to FIG. 1A and[blocks 100-105 and 130-145] of FIGS. 1B-1E, pertains to an examplemethod of importing into 3D computer generated jig models 38 3D computergenerated surface models 40 of arthroplasty target areas 42 of 3Dcomputer generated arthritic models 36 of the patient's joint bones. Theresulting “jig data” 46 is used to produce a jig customized to matinglyreceive the arthroplasty target areas of the respective bones of thepatient's joint.

The third section, which is discussed with respect to FIG. 1A and[blocks 150-165] of FIG. 1E, pertains to a method of combining orintegrating the “saw cut and drill hole data” 44 with the “jig data” 46to result in “integrated jig data” 48. The “integrated jig data” 48 isprovided to the CNC machine 10 for the production of customizedarthroplasty jigs 2 from jig blanks 50 provided to the CNC machine 10.The resulting customized arthroplasty jigs 2 include saw cut slots anddrill holes positioned in the jigs 2 such that when the jigs 2 matinglyreceive the arthroplasty target areas of the patient's bones, the cutslots and drill holes facilitate preparing the arthroplasty target areasin a manner that allows the arthroplasty joint implants to generallyrestore the patient's joint line to its pre-degenerated or naturalalignment state.

As shown in FIG. 1A, the system 4 includes a computer 6 having a CPU 7,a monitor or screen 9 and an operator interface controls 11. Thecomputer 6 is linked to a medical imaging system 8, such as a CT or MRImachine 8, and a computer controlled machining system 10, such as a CNCmilling machine 10.

As indicated in FIG. 1A, a patient 12 has a joint 14 (e.g., a knee,elbow, ankle, wrist, hip, shoulder, skull/vertebrae orvertebrae/vertebrae interface, etc.) to be replaced. The patient 12 hasthe joint 14 scanned in the imaging machine 8. The imaging machine 8makes a plurality of scans of the joint 14, wherein each scan pertainsto a thin slice of the joint 14.

As can be understood from FIG. 1B, the plurality of scans is used togenerate a plurality of two-dimensional (“2D”) images 16 of the joint 14[block 100]. Where, for example, the joint 14 is a knee 14, the 2Dimages will be of the femur 18 and tibia 20. The imaging may beperformed via CT or MRI. In one embodiment employing MRI, the imagingprocess may be as disclosed in U.S. patent application Ser. No.11/946,002 to Park, which is entitled “Generating MRI Images Usable ForThe Creation Of 3D Bone Models Employed To Make Customized ArthroplastyJigs,” was filed Nov. 27, 2007 and is incorporated by reference in itsentirety into this Detailed Description.

As can be understood from FIG. 1A, the 2D images are sent to thecomputer 6 for creating computer generated 3D models. As indicated inFIG. 1B, in one embodiment, point P is identified in the 2D images 16[block 105]. In one embodiment, as indicated in [block 105] of FIG. 1A,point P may be at the approximate medial-lateral and anterior-posteriorcenter of the patient's joint 14. In other embodiments, point P may beat any other location in the 2D images 16, including anywhere on, nearor away from the bones 18, 20 or the joint 14 formed by the bones 18,20.

As described later in this overview, point P may be used to locate thecomputer generated 3D models 22, 28, 36 created from the 2D images 16and to integrate information generated via the 3D models. Depending onthe embodiment, point P, which serves as a position and/or orientationreference, may be a single point, two points, three points, a point plusa plane, a vector, etc., so long as the reference P can be used toposition and/or orient the 3D models 22, 28, 36 generated via the 2Dimages 16.

As shown in FIG. 1C, the 2D images 16 are employed to create computergenerated 3D bone-only (i.e., “bone models”) 22 of the bones 18, 20forming the patient's joint 14 [block 110]. The bone models 22 arelocated such that point P is at coordinates (X_(0-j), Y_(0-j), Z_(0-j))relative to an origin (X₀, Y₀, Z₀) of an X-Y-Z axis [block 110]. Thebone models 22 depict the bones 18, 20 in the present deterioratedcondition with their respective degenerated joint surfaces 24, 26, whichmay be a result of osteoarthritis, injury, a combination thereof, etc.

Computer programs for creating the 3D computer generated bone models 22from the 2D images 16 include: Analyze from AnalyzeDirect, Inc.,Overland Park, Kans.; Insight Toolkit, an open-source software availablefrom the National Library of Medicine Insight Segmentation andRegistration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-sourcesoftware available from www.slicer.org; Mimics from Materialise, AnnArbor, Mich.; and Paraview available at www.paraview.org.

As indicated in FIG. 1C, the 3D computer generated bone models 22 areutilized to create 3D computer generated “restored bone models” or“planning bone models” 28 wherein the degenerated surfaces 24, 26 aremodified or restored to approximately their respective conditions priorto degeneration [block 115]. Thus, the bones 18, 20 of the restored bonemodels 28 are reflected in approximately their condition prior todegeneration. The restored bone models 28 are located such that point Pis at coordinates (X_(0-j), Y_(0-j), Z_(0-j)) relative to the origin(X₀, Y₀, Z₀). Thus, the restored bone models 28 share the sameorientation and positioning relative to the origin (X₀, Y₀, Z₀) as thebone models 22.

In one embodiment, the restored bone models 28 are manually created fromthe bone models 22 by a person sitting in front of a computer 6 andvisually observing the bone models 22 and their degenerated surfaces 24,26 as 3D computer models on a computer screen 9. The person visuallyobserves the degenerated surfaces 24, 26 to determine how and to whatextent the degenerated surfaces 24, 26 surfaces on the 3D computer bonemodels 22 need to be modified to restore them to their pre-degeneratedcondition. By interacting with the computer controls 11, the person thenmanually manipulates the 3D degenerated surfaces 24, 26 via the 3Dmodeling computer program to restore the surfaces 24, 26 to a state theperson believes to represent the pre-degenerated condition. The resultof this manual restoration process is the computer generated 3D restoredbone models 28, wherein the surfaces 24′, 26′ are indicated in anon-degenerated state.

In one embodiment, the above-described bone restoration process isgenerally or completely automated. In other words, a computer programmay analyze the bone models 22 and their degenerated surfaces 24, 26 todetermine how and to what extent the degenerated surfaces 24, 26surfaces on the 3D computer bone models 22 need to be modified torestore them to their pre-degenerated condition. The computer programthen manipulates the 3D degenerated surfaces 24, 26 to restore thesurfaces 24, 26 to a state intended to represent the pre-degeneratedcondition. The result of this automated restoration process is thecomputer generated 3D restored bone models 28, wherein the surfaces 24′,26′ are indicated in a non-degenerated state.

As depicted in FIG. 1C, the restored bone models 28 are employed in apre-operative planning (“POP”) procedure to determine saw cut locations30 and drill hole locations 32 in the patient's bones that will allowthe arthroplasty joint implants to generally restore the patient's jointline to it pre-degenerative alignment [block 120].

In one embodiment, the POP procedure is a manual process, whereincomputer generated 3D implant models 34 (e.g., femur and tibia implantsin the context of the joint being a knee) and restored bone models 28are manually manipulated relative to each other by a person sitting infront of a computer 6 and visually observing the implant models 34 andrestored bone models 28 on the computer screen 9 and manipulating themodels 28, 34 via the computer controls 11. By superimposing the implantmodels 34 over the restored bone models 28, or vice versa, the jointsurfaces of the implant models 34 can be aligned or caused to correspondwith the joint surfaces of the restored bone models 28. By causing thejoint surfaces of the models 28, 34 to so align, the implant models 34are positioned relative to the restored bone models 28 such that the sawcut locations 30 and drill hole locations 32 can be determined relativeto the restored bone models 28.

In one embodiment, the POP process is generally or completely automated.For example, a computer program may manipulate computer generated 3Dimplant models 34 (e.g., femur and tibia implants in the context of thejoint being a knee) and restored bone models or planning bone models 28relative to each other to determine the saw cut and drill hole locations30, 32 relative to the restored bone models 28. The implant models 34may be superimposed over the restored bone models 28, or vice versa. Inone embodiment, the implant models 34 are located at point P′ (X_(0-k))Y_(0-k)) Z_(0-k)) relative to the origin (X₀, Y₀, Z₀), and the restoredbone models 28 are located at point P (X_(0-j), Y_(0-j), Z_(0-j)). Tocause the joint surfaces of the models 28, 34 to correspond, thecomputer program may move the restored bone models 28 from point P(X_(0-j), Y_(0-j), Z_(0-j)) to point P′ (X_(0-k)) Y_(0-k)) Z_(0-k)), orvice versa. Once the joint surfaces of the models 28, 34 are in closeproximity, the joint surfaces of the implant models 34 may beshape-matched to align or correspond with the joint surfaces of therestored bone models 28. By causing the joint surfaces of the models 28,34 to so align, the implant models 34 are positioned relative to therestored bone models 28 such that the saw cut locations 30 and drillhole locations 32 can be determined relative to the restored bone models28.

As indicated in FIG. 1E, in one embodiment, the data 44 regarding thesaw cut and drill hole locations 30, 32 relative to point P′ (X_(0-k),Y_(0-k), Z_(0-k)) is packaged or consolidated as the “saw cut and drillhole data” 44 [block 145]. The “saw cut and drill hole data” 44 is thenused as discussed below with respect to [block 150] in FIG. 1E.

As can be understood from FIG. 1D, the 2D images 16 employed to generatethe bone models 22 discussed above with respect to [block 110] of FIG.1C are also used to create computer generated 3D bone and cartilagemodels (i.e., “arthritic models”) 36 of the bones 18, 20 forming thepatient's joint 14 [block 130]. Like the above-discussed bone models 22,the arthritic models 36 are located such that point P is at coordinates(X_(0-j), Y_(0-j), Z_(0-j)) relative to the origin (X₀, Y₀, Z₀) of theX-Y-Z axis [block 130]. Thus, the bone and arthritic models 22, 36 sharethe same location and orientation relative to the origin (X₀, Y₀, Z₀).This position/orientation relationship is generally maintainedthroughout the process discussed with respect to FIGS. 1B-1E.Accordingly, movements relative to the origin (X₀, Y₀, Z₀) of the bonemodels 22 and the various descendants thereof (i.e., the restored bonemodels 28, bone cut locations 30 and drill hole locations 32) are alsoapplied to the arthritic models 36 and the various descendants thereof(i.e., the jig models 38). Maintaining the position/orientationrelationship between the bone models 22 and arthritic models 36 andtheir respective descendants allows the “saw cut and drill hole data” 44to be integrated into the “jig data” 46 to form the “integrated jigdata” 48 employed by the CNC machine 10 to manufacture the customizedarthroplasty jigs 2.

Computer programs for creating the 3D computer generated arthriticmodels 36 from the 2D images 16 include: Analyze from AnalyzeDirect,Inc., Overland Park, Kans.; Insight Toolkit, an open-source softwareavailable from the National Library of Medicine Insight Segmentation andRegistration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-sourcesoftware available from www.slicer.org; Mimics from Materialise, AnnArbor, Mich.; and Paraview available at www.paraview.org.

Similar to the bone models 22, the arthritic models 36 depict the bones18, in the present deteriorated condition with their respectivedegenerated joint surfaces 24, 26, which may be a result ofosteoarthritis, injury, a combination thereof, etc. However, unlike thebone models 22, the arthritic models 36 are not bone-only models, butinclude cartilage in addition to bone. Accordingly, the arthritic models36 depict the arthroplasty target areas 42 generally as they will existwhen the customized arthroplasty jigs 2 matingly receive thearthroplasty target areas 42 during the arthroplasty surgical procedure.

As indicated in FIG. 1D and already mentioned above, to coordinate thepositions/orientations of the bone and arthritic models 36, 36 and theirrespective descendants, any movement of the restored bone models 28 frompoint P to point P′ is tracked to cause a generally identicaldisplacement for the “arthritic models” 36 [block 135].

As depicted in FIG. 1D, computer generated 3D surface models 40 of thearthroplasty target areas 42 of the arthritic models 36 are importedinto computer generated 3D arthroplasty jig models 38 [block 140]. Thus,the jig models 38 are configured or indexed to matingly receive thearthroplasty target areas 42 of the arthritic models 36. Jigs 2manufactured to match such jig models 38 will then matingly receive thearthroplasty target areas of the actual joint bones during thearthroplasty surgical procedure.

In some embodiments, the 3D surface models 40 may be modified to accountfor irregularities in the patient's bone anatomy or limitations in theimaging process. For example, the 3D surface models 40 may be subjectedto, or the result of, an “overestimation” process. The “overestimated”3D surface models 40 may result in bone mating surfaces of the actualjigs that matingly receive and contact certain portions of thearthroplasty target areas of the actual joint bones while other portionsof the jigs are spaced apart from the bones, including, for example,some regions of the arthroplasty target areas of the actual joint bones.Thus, the bone mating surfaces of the actual jigs may matingly contactcertain specific portions of the arthroplasty target areas of the actualjoint bones while other areas of the arthroplasty target areas are notmatingly contacted. In some embodiments, the specific portions of thearthroplasty target areas contacted by the jig's bone mating surfacesmay be those areas that are most likely to be accurately 3D computermodeled and most likely to result in a reliably accurate mating contactbetween the jig's bone mating surface and the arthroplasty target areas,and the portions of the arthroplasty target areas not contacted by thejig's bone mating surfaces may be those areas that are the least likelyto be accurately 3D computer modeled.

In other words, for some embodiments, overestimation may result in areasof mating contact for the bone mating surfaces of the actual jigs beingbased on the areas of the 3D surface models that are most reliablyaccurate with respect to the image scan data and most readily machinedvia the tooling of the CNC machine. Conversely, for some embodiments,overestimation may result in areas of non-contact for the bone mating orother surfaces of the actual jigs for those areas of the jig pertainingto those areas of the 3D surface models that result from image scan datathat is less accurate or reliable and/or represent bone features thatare too small to be readily machined via the tooling of the CNC machine.The result of the overestimation process described below is actual jigswith a bone mating surfaces that matingly contact certain reliableregions of the arthroplasty target areas of the actual joint bones whileavoiding contact with certain less reliable regions of the arthroplastytarget areas, resulting in jigs with bone mating surfaces thataccurately and reliably matingly receive the arthroplasty targetregions.

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is a manual process. The 3D computergenerated models 36, 38 are manually manipulated relative to each otherby a person sitting in front of a computer 6 and visually observing thejig models 38 and arthritic models 36 on the computer screen 9 andmanipulating the models 36, 38 by interacting with the computer controls11. In one embodiment, by superimposing the jig models 38 (e.g., femurand tibia arthroplasty jigs in the context of the joint being a knee)over the arthroplasty target areas 42 of the arthritic models 36, orvice versa, the surface models 40 of the arthroplasty target areas 42can be imported into the jig models 38, resulting in jig models 38indexed to matingly receive the arthroplasty target areas 42 of thearthritic models 36. Point P′ (X_(0-k), Y_(0-k), Z_(0-k)) can also beimported into the jig models 38, resulting in jig models 38 positionedand oriented relative to point P′ (X_(0-k), Y_(0-k), Z_(0-k)) to allowtheir integration with the bone cut and drill hole data 44 of [block125].

In one embodiment, the procedure for indexing the jig models 38 to thearthroplasty target areas 42 is generally or completely automated, asdiscussed in detail later in this Detailed Description. For example, acomputer program may create 3D computer generated surface models 40 ofthe arthroplasty target areas 42 of the arthritic models 36. Thecomputer program may then import the surface models 40 and point P′(X_(0-k), Y_(0-k), Z_(0-k)) into the jig models 38, resulting in the jigmodels 38 being indexed to matingly receive the arthroplasty targetareas 42 of the arthritic models 36. In some embodiments, the surfacemodels 40 may include accounting for irregularities in the patient'sbone anatomy and/or limitations in the imaging technology by creatingdeliberate gaps between the jig's surface and the patient's bone. Theresulting jig models 38 are also positioned and oriented relative topoint P′ (X_(0-k), Y_(0-k), Z_(0-k)) to allow their integration with thebone cut and drill hole data 44 of [block 125].

In one embodiment, the arthritic models 36 may be 3D volumetric modelsas generated from the closed-loop process discussed below with respectto FIGS. 2D-2F. In other embodiments, the arthritic models 36 may be 3Dsurface models as generated from the open-loop process discussed belowwith respect to FIGS. 2A-2C and 12A-12C.

As indicated in FIG. 1E, in one embodiment, the data regarding the jigmodels 38 and surface models 40 relative to point P′ (X_(0-k)) Y_(0-k))Z_(0-k)) is packaged or consolidated as the “jig data” 46 [block 145].The “jig data” 46 is then used as discussed below with respect to [block150] in FIG. 1E.

As can be understood from FIG. 1E, the “saw cut and drill hole data” 44is integrated with the “jig data” 46 to result in the “integrated jigdata” 48 [block 150]. As explained above, since the “saw cut and drillhole data” 44, “jig data” 46 and their various ancestors (e.g., models22, 28, 36, 38) are matched to each other for position and orientationrelative to point P and P′, the “saw cut and drill hole data” 44 isproperly positioned and oriented relative to the “jig data” 46 forproper integration into the “jig data” 46. The resulting “integrated jigdata” 48, when provided to the CNC machine 10, results in jigs 2: (1)configured to matingly receive the arthroplasty target areas of thepatient's bones; and (2) having cut slots and drill holes thatfacilitate preparing the arthroplasty target areas in a manner thatallows the arthroplasty joint implants to generally restore thepatient's joint line to its pre-degenerated or natural alignment state.

As can be understood from FIGS. 1A and 1E, the “integrated jig data” 48is transferred from the computer 6 to the CNC machine 10 [block 155].Jig blanks 50 are provided to the CNC machine 10 [block 160], and theCNC machine 10 employs the “integrated jig data” to machine thearthroplasty jigs 2 from the jig blanks 50.

For a discussion of example customized arthroplasty cutting jigs 2capable of being manufactured via the above-discussed process, referenceis made to FIGS. 1F-1I. While, as pointed out above, the above-discussedprocess may be employed to manufacture jigs 2 configured forarthroplasty procedures involving knees, elbows, ankles, wrists, hips,shoulders, vertebra interfaces, etc., the jig examples depicted in FIGS.1F-1I are for total knee replacement (“TKR”) procedures. Thus, FIGS. 1Fand 1G are, respectively, bottom and top perspective views of an examplecustomized arthroplasty femur jig 2A, and FIGS. 1H and 1I are,respectively, bottom and top perspective views of an example customizedarthroplasty tibia jig 2B.

As indicated in FIGS. 1F and 1G, a femur arthroplasty jig 2A may includean interior side or portion 100 and an exterior side or portion 102.When the femur cutting jig 2A is used in a TKR procedure, the interiorside or portion 100 faces and matingly receives the arthroplasty targetarea 42 of the femur lower end, and the exterior side or portion 102 ison the opposite side of the femur cutting jig 2A from the interiorportion 100.

The interior portion 100 of the femur jig 2A is configured to match thesurface features of the damaged lower end (i.e., the arthroplasty targetarea 42) of the patient's femur 18. Thus, when the target area 42 isreceived in the interior portion 100 of the femur jig 2A during the TKRsurgery, the surfaces of the target area 42 and the interior portion 100match.

The surface of the interior portion 100 of the femur cutting jig 2A ismachined or otherwise formed into a selected femur jig blank 50A and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged lower end or target area 42 of the patient's femur 18. In someembodiments, the 3D surface model 40 may modified via the“overestimation” process described below to account for limitations inthe medical imaging process and/or limitations in the machining process.

As indicated in FIGS. 1H and 1I, a tibia arthroplasty jig 2B may includean interior side or portion 104 and an exterior side or portion 106.When the tibia cutting jig 2B is used in a TKR procedure, the interiorside or portion 104 faces and matingly receives the arthroplasty targetarea 42 of the tibia upper end, and the exterior side or portion 106 ison the opposite side of the tibia cutting jig 2B from the interiorportion 104.

The interior portion 104 of the tibia jig 2B is configured to match thesurface features of the damaged upper end (i.e., the arthroplasty targetarea 42) of the patient's tibia 20. Thus, when the target area 42 isreceived in the interior portion 104 of the tibia jig 2B during the TKRsurgery, the surfaces of the target area 42 and the interior portion 104match.

The surface of the interior portion 104 of the tibia cutting jig 2B ismachined or otherwise formed into a selected tibia jig blank 50B and isbased or defined off of a 3D surface model 40 of a target area 42 of thedamaged upper end or target area 42 of the patient's tibia 20. In someembodiments, the 3D surface model 40 may modified via the“overestimation” process described below to account for limitations inthe medical imaging process and/or limitations in the machining process.

b. Overview of Automated Process for Indexing 3D Arthroplasty Jig Modelsto Arthroplasty Target Areas

As mentioned above with respect to [block 140] of FIG. 1D, the processfor indexing the 3D arthroplasty jig models 38 to the arthroplastytarget areas 42 can be automated. A discussion of an example of such anautomated process will now concern the remainder of this DetailedDescription, beginning with an overview of the automated indexingprocess.

As can be understood from FIG. 1A and [blocks 100-105] of FIG. 1B, apatient 12 has a joint 14 (e.g., a knee, elbow, ankle, wrist, shoulder,hip, vertebra interface, etc.) to be replaced. The patient 12 has thejoint 14 scanned in an imaging machine 8 (e.g., a CT, MRI, etc. machine)to create a plurality of 2D scan images 16 of the bones (e.g., femur 18and tibia 20) forming the patient's joint 14 (e.g., knee). Each scanimage 16 is a thin slice image of the targeted bone(s) 18, 20. The scanimages 16 are sent to the CPU 7, which employs an open-loop imageanalysis along targeted features 42 of the scan images 16 of the bones18, 20 to generate a contour line for each scan image 16 along theprofile of the targeted features 42.

As can be understood from FIG. 1A and [block 110] of FIG. 1C, the CPU 7compiles the scan images 16 and, more specifically, the contour lines togenerate 3D computer surface models (“arthritic models”) 36 of thetargeted features 42 of the patient's joint bones 18, 20. In the contextof total knee replacement (“TKR”) surgery, the targeted features 42 maybe the lower or knee joint end of the patient's femur 18 and the upperor knee joint end of the patient's tibia 20. More specifically, thetargeted features 42 may be the tibia contacting articulating surface ofthe patient's femur 18 and the femur contacting articulating surface ofthe patient's tibia 20.

In some embodiments, the “arthritic models” 36 may be surface models orvolumetric solid models respectively formed via an open-loop orclosed-loop process such that the contour lines are respectively open orclosed loops. In one embodiment discussed in detail herein, the“arthritic models” 36 may be surface models formed via an open-loopprocess. By employing an open-loop and surface model approach, asopposed to a closed-loop and volumetric solid model approach, thecomputer modeling process requires less processing capability and timefrom the CPU 7 and, as a result, is more cost effective.

The system 4 measures the anterior-posterior extent and medial-lateralextent of the target areas 42 of the “arthritic models” 36. Theanterior-posterior extent and medial-lateral extent may be used todetermine an aspect ratio, size and/or configuration for the 3D“arthritic models” 36 of the respective bones 18, 20. In one embodimentof a jig blank grouping and selection method discussed below, the aspectratio, size and/or configuration of the 3D “arthritic models” 36 of therespective bones 18, 20 may be used for comparison to the aspect ratio,size and/or configuration of 3D computer models of candidate jig blanks50 in a jig blank grouping and selection method discussed below. In oneembodiment of a jig blank grouping and selection method discussed below,the anterior-posterior and medial-lateral dimensions of the 3D“arthritic models” 36 of the respective bones 18, 20 may be used forcomparison to the anterior-posterior and medial-lateral dimensions of 3Dcomputer models of candidate jig blanks 50.

In the context of TKR, the jigs 2 will be femur and tibia arthroplastycutting jigs 2A, 2B, which are machined or otherwise formed from femurand tibia jig blanks 50A, 50B. A plurality of candidate jig blank sizesexists, for example, in a jig blank library. While each candidate jigblank may have a unique combination of anterior-posterior andmedial-lateral dimension sizes, in some embodiments, two or more of thecandidate jig blanks may share a common aspect ratio or configuration.The candidate jig blanks of the library may be grouped along slopedlines of a plot according to their aspect ratios. The system 4 employsthe jig blank grouping and selection method to select a jig blank 50from a plurality of available jig blank sizes contained in the jig blanklibrary. For example, the configurations, sizes and/or aspect ratios ofthe tibia and femur 3D arthritic models 36 are compared to theconfigurations, sizes and/or aspect ratios of the 3D models of thecandidate jig blanks with or without a dimensional comparison betweenthe arthritic models 36 and the models of the candidate jig blanks.

Alternatively, in one embodiment, the anterior-posterior andmedial-lateral dimensions of the target areas of the arthritic models 36of the patient's femur and tibia 18, 20 are increased via a mathematicalformula. The resulting mathematically modified anterior-posterior andmedial-lateral dimensions are then compared to the anterior-posteriorand medial-lateral dimensions of the models of the candidate jig blanks50A, 50B. In one embodiment, the jig blanks 50A, 50B selected are thejig blanks having anterior-posterior and medial-lateral dimensions thatare the closest in size to the mathematically modifiedanterior-posterior and medial-lateral dimensions of the patient's bones18, 20 without being exceeded by the mathematically modified dimensionsof the patient's bones 18, 20. In one embodiment, the jig blankselection method results in the selection of a jig blank 50 that is asnear as possible in size to the patient's knee features, therebyminimizing the machining involved in creating a jig 2 from a jig blank.

In one embodiment, as discussed with respect to FIGS. 1F-1I, eacharthroplasty cutting jig 2 includes an interior portion and an exteriorportion. The interior portion is dimensioned specific to the surfacefeatures of the patient's bone that are the focus of the arthroplasty.Thus, where the arthroplasty is for TKR surgery, the jigs will be afemur jig and/or a tibia jig. The femur jig will have an interiorportion custom configured to match the damaged surface of the lower orjoint end of the patient's femur. The tibia jig will have an interiorportion custom configured to match the damaged surface of the upper orjoint end of the patient's tibia.

In one embodiment, because of the jig blank grouping and selectionmethod, the exterior portion of each arthroplasty cutting jig 2 issubstantially similar in size to the patient's femur and tibia 3Darthritic models 36. However, to provide adequate structural integrityfor the cutting jigs 2, the exterior portions of the jigs 2 may bemathematically modified to cause the exterior portions of the jigs 2 toexceed the 3D femur and tibia models in various directions, therebyproviding the resulting cutting jigs 2 with sufficient jig materialbetween the exterior and interior portions of the jigs 2 to provideadequate structural strength.

As can be understood from [block 140] of FIG. 1D, once the system 4selects femur and tibia jig blanks 50 of sizes and configurationssufficiently similar to the sizes and configurations of the patient'sfemur and tibia computer arthritic models 36, the system 4 superimposesthe 3D computer surface models 40 of the targeted features 42 of thefemur 18 and tibia 20 onto the interior portion of the respective 3Dcomputer models of the selected femur and tibia jigs 38, or moreappropriately in one version of the present embodiment, the jig blanks50. The result, as can be understood from [block 145] of FIG. 1E, iscomputer models of the femur and tibia jigs 2 in the form of “jig data”46, wherein the femur and tibia jig computer models have: (1) respectiveexterior portions closely approximating the overall size andconfiguration of the patient's femur and tibia; and (2) respectiveinterior portions having surfaces that match the targeted features 42 ofthe patient's femur 18 and tibia 20.

The system 4 employs the data from the jig computer models (i.e., “jigdata” 46) to cause the CNC machine 10 to machine the actual jigs 2 fromactual jig blanks. The result is the automated production of actualfemur and tibia jigs 2 having: (1) exterior portions generally matchingthe patient's actual femur and tibia with respect to size and overallconfiguration; and (2) interior portions having patient-specificdimensions and configurations corresponding to the actual dimensions andconfigurations of the targeted features 42 of the patient's femur andtibia. The systems 4 and methods disclosed herein allow for theefficient manufacture of arthroplasty jigs 2 customized for the specificbone features of a patient.

The jigs 2 and systems 4 and methods of producing such jigs areillustrated herein in the context of knees and TKR surgery. However,those skilled in the art will readily understand the jigs 2 and system 4and methods of producing such jigs can be readily adapted for use in thecontext of other joints and joint replacement surgeries, e.g., elbows,shoulders, hips, etc. Accordingly, the disclosure contained hereinregarding the jigs 2 and systems 4 and methods of producing such jigsshould not be considered as being limited to knees and TKR surgery, butshould be considered as encompassing all types of joint surgeries.

c. Defining a 3D Surface Model of an Arthroplasty Target Area of a FemurLower End for Use as a Surface of an Interior Portion of a FemurArthroplasty Cutting Jig.

For a discussion of a method of generating a 3D model 40 of a targetarea 42 of a damaged lower end 204 of a patient's femur 18, reference ismade to FIGS. 2A-2G. FIG. 2A is an anterior-posterior (“AP”) image slice208 of the damaged lower or knee joint end 204 of the patient's femur18, wherein the image slice 208 includes an open-loop contour linesegment 210 corresponding to the target area 42 of the damaged lower end204. FIG. 2B is a plurality of image slices (16-1, 16-1, 16-2, . . .16-n) with their respective open-loop contour line segments (210-1,210-2, . . . 210-n), the open-loop contour line segments 210 beingaccumulated to generate the 3D model 40 of the target area 42. FIG. 2Cis a 3D model 40 of the target area 42 of the damaged lower end 204 asgenerated using the open-loop contour line segments (16-1, 16-2, . . .16-n) depicted in FIG. 2B. FIGS. 2D-2F are respectively similar to FIGS.2A-2C, except FIGS. 2D-2F pertain to a closed-loop contour line asopposed to an open-loop contour line. FIG. 2G is a flow chartillustrating an overview of the method of producing a femur jig 2A.

As can be understood from FIGS. 1A, 1B and 2A, the imager 8 is used togenerate a 2D image slice 16 of the damaged lower or knee joint end 204of the patient's femur 18. As depicted in FIG. 2A, the 2D image 16 maybe an AP view of the femur 18. Depending on whether the imager 8 is aMRI or CT imager, the image slice 16 will be a MRI or CT slice. Thedamaged lower end 204 includes the posterior condyle 212, an anteriorfemur shaft surface 214, and an area of interest or targeted area 42that extends from the posterior condyle 212 to the anterior femur shaftsurface 214. The targeted area 42 of the femur lower end may be thearticulating contact surfaces of the femur lower end that contactcorresponding articulating contact surfaces of the tibia upper or kneejoint end.

As shown in FIG. 2A, the image slice 16 may depict the cancellous bone216, the cortical bone 218 surrounding the cancellous bone, and thearticular cartilage lining portions of the cortical bone 218. Thecontour line 210 may extend along the targeted area 42 and immediatelyadjacent the cortical bone and cartilage to outline the contour of thetargeted area 42 of the femur lower end 204. The contour line 210extends along the targeted area 42 starting at point A on the posteriorcondyle 212 and ending at point B on the anterior femur shaft surface214.

In one embodiment, as indicated in FIG. 2A, the contour line 210 extendsalong the targeted area 42, but not along the rest of the surface of thefemur lower end 204. As a result, the contour line 210 forms anopen-loop that, as will be discussed with respect to FIGS. 2B and 2C,can be used to form an open-loop region or 3D computer model 40, whichis discussed with respect to [block 140] of FIG. 1D and closely matchesthe 3D surface of the targeted area 42 of the femur lower end. Thus, inone embodiment, the contour line is an open-loop and does not outlinethe entire cortical bone surface of the femur lower end 204. Also, inone embodiment, the open-loop process is used to form from the 3D images16 a 3D surface model 36 that generally takes the place of the arthriticmodel 36 discussed with respect to [blocks 125-140] of FIG. 1D and whichis used to create the surface model 40 used in the creation of the “jigdata” 46 discussed with respect to [blocks 145-150] of FIG. 1E.

In one embodiment and in contrast to the open-loop contour line 210depicted in FIGS. 2A and 2B, the contour line is a closed-loop contourline 210′ that outlines the entire cortical bone surface of the femurlower end and results in a closed-loop area, as depicted in FIG. 2D. Theclosed-loop contour lines 210′-2, . . . 210′-n of each image slice 16-1,. . . 16-n are combined, as indicated in FIG. 2E. A closed-loop area mayrequire the analysis of the entire surface region of the femur lower end204 and result in the formation of a 3D model of the entire femur lowerend 204 as illustrated in FIG. 2F. Thus, the 3D surface model resultingfrom the closed-loop process ends up having in common much, if not all,the surface of the 3D arthritic model 36. In one embodiment, theclosed-loop process may result in a 3D volumetric anatomical joint solidmodel from the 2D images 16 via applying mathematical algorithms. U.S.Pat. No. 5,682,886, which was filed Dec. 26, 1995 and is incorporated byreference in its entirety herein, applies a snake algorithm forming acontinuous boundary or closed-loop. After the femur has been outlined, amodeling process is used to create the 3D surface model, for example,through a Bezier patches method. Other 3D modeling processes, e.g.,commercially-available 3D construction software as listed in other partsof this Detailed Description, are applicable to 3D surface modelgeneration for closed-loop, volumetric solid modeling.

In one embodiment, the closed-loop process is used to form from the 3Dimages 16 a 3D volumetric solid model 36 that is essentially the same asthe arthritic model 36 discussed with respect to [blocks 125-140] ofFIG. 1D. The 3D volumetric solid model 36 is used to create the surfacemodel 40 used in the creation of the “jig data” 46 discussed withrespect to [blocks 145-150] of FIG. 1E.

The formation of a 3D volumetric solid model of the entire femur lowerend employs a process that may be much more memory and time intensivethan using an open-loop contour line to create a 3D model of thetargeted area 42 of the femur lower end. Accordingly, although theclosed-loop methodology may be utilized for the systems and methodsdisclosed herein, for at least some embodiments, the open-loopmethodology may be preferred over the closed-loop methodology.

An example of a closed-loop methodology is disclosed in U.S. patentapplication Ser. No. 11/641,569 to Park, which is entitled “ImprovedTotal Joint Arthroplasty System” and was filed Jan. 19, 2007. Thisapplication is incorporated by reference in its entirety into thisDetailed Description.

As can be understood from FIGS. 2B and 2G, the imager 8 generates aplurality of image slices (16-1, 16-2 . . . 16-n) via repetitive imagingoperations [block 1000]. Each image slice 16 has an open-loop contourline (210-1, 210-2 . . . 210-n) extending along the targeted region 42in a manner as discussed with respect to FIG. 2A [block 1005]. In oneembodiment, each image slice is a two-millimeter 2D image slice 16. Thesystem 4 compiles the plurality of 2D image slices (16-1, 16-2 . . .16-n) and, more specifically, the plurality of open-loop contour lines(210-1, 210-2, . . . 210-n) into the 3D femur surface computer model 40depicted in FIG. 2C [block 1010]. This process regarding the generationof the surface model 40 is also discussed in the overview section withrespect to [blocks 100-105] of FIG. 1B and [blocks 130-140] of FIG. 1D.A similar process may be employed with respect to the closed-loopcontour lines depicted in FIGS. 2D-2F.

As can be understood from FIG. 2C, the 3D femur surface computer model40 is a 3D computer representation of the targeted region 42 of thefemur lower end. In one embodiment, the 3D representation of thetargeted region 42 is a 3D representation of the articulated tibiacontact surfaces of the femur distal end. As the open-loop generated 3Dmodel 40 is a surface model of the relevant tibia contacting portions ofthe femur lower end, as opposed to a 3D model of the entire surface ofthe femur lower end as would be a result of a closed-loop contour line,the open-loop generated 3D model 40 is less time and memory intensive togenerate.

In one embodiment, the open-loop generated 3D model 40 is a surfacemodel of the tibia facing end face of the femur lower end, as opposed a3D model of the entire surface of the femur lower end. The 3D model 40can be used to identify the area of interest or targeted region 42,which, as previously stated, may be the relevant tibia contactingportions of the femur lower end. Again, the open-loop generated 3D model40 is less time and memory intensive to generate as compared to a 3Dmodel of the entire surface of the femur distal end, as would begenerated by a closed-loop contour line. Thus, for at least someversions of the embodiments disclosed herein, the open-loop contour linemethodology is preferred over the closed-loop contour line methodology.However, the system 4 and method disclosed herein may employ either theopen-loop or closed-loop methodology and should not be limited to one orthe other.

Regardless of whether the 3D model 40 is a surface model of the targetedregion 42 (i.e., a 3D surface model generated from an open-loop processand acting as the arthritic model 22) or the entire tibia facing endface of the femur lower end (i.e., a 3D volumetric solid model generatedfrom a closed-loop process and acting as the arthritic model 22), thedata pertaining to the contour lines 210 can be converted into the 3Dcontour computer model 40 via the surface rendering techniques disclosedin any of the aforementioned U.S. patent applications to Park. Forexample, surface rending techniques employed include point-to-pointmapping, surface normal vector mapping, local surface mapping, andglobal surface mapping techniques. Depending on the situation, one or acombination of mapping techniques can be employed.

In one embodiment, the generation of the 3D model 40 depicted in FIG. 2Cmay be formed by using the image slices 16 to determine locationcoordinate values of each of a sequence of spaced apart surface pointsin the open-loop region of FIG. 2B. A mathematical model may then beused to estimate or compute the 3D model 40 in FIG. 2C. Examples ofother medical imaging computer programs that may be used include, butare not limited to: Analyze from AnalyzeDirect, Inc. of Overland Park,Kans.; open-source software such as Paraview of Kitware, Inc.; InsightToolkit (“ITK”) available at www.itk.org; 3D Slicer available atwww.slicer.org; and Mimics from Materialise of Ann Arbor, Mich.

Alternatively or additionally to the aforementioned systems forgenerating the 3D model 40 depicted in FIG. 2C, other systems forgenerating the 3D model 40 of FIG. 2C include the surface renderingtechniques of the Non-Uniform Rational B-spline (“NURB”) program or theBézier program. Each of these programs may be employed to generate the3D contour model 40 from the plurality of contour lines 210.

In one embodiment, the NURB surface modeling technique is applied to theplurality of image slices 16 and, more specifically, the plurality ofopen-loop contour lines 210 of FIG. 2B. The NURB software generates a 3Dmodel 40 as depicted in FIG. 2C, wherein the 3D model 40 has areas ofinterest or targeted regions 42 that contain both a mesh and its controlpoints. For example, see Ervin et al., Landscape Modeling, McGraw-Hill,2001, which is hereby incorporated by reference in its entirety intothis Detailed Description.

In one embodiment, the NURB surface modeling technique employs thefollowing surface equation:

${{G\left( {s,t} \right)} = \frac{\sum\limits_{i = 0}^{k\; 1}{\sum\limits_{j = 0}^{k\; 2}{{W\left( {i,j} \right)}{P\left( {i,j} \right)}{b_{i}(s)}{b_{j}(t)}}}}{\sum\limits_{i = 0}^{k\; 1}{\sum\limits_{j = 0}^{k\; 2}{{W\left( {i,j} \right)}{b_{i}(s)}{b_{j}(t)}}}}},$wherein P(i,j) represents a matrix of vertices with nrows=(k1+1) andncols=(k2+1), W(i,j) represents a matrix of vertex weights of one pervertex point, b_(i)(s) represents a row-direction basis or blending ofpolynomial functions of degree M1, b_(j)(t) represents acolumn-direction basis or blending polynomial functions of degree M2, srepresents a parameter array of row-direction knots, and t represents aparameter array of column-direction knots.

In one embodiment, the Bézier surface modeling technique employs theBézier equation (1972, by Pierre Bézier) to generate a 3D model 40 asdepicted in FIG. 2C, wherein the model 40 has areas of interest ortargeted regions 42. A given Bézier surface of order (n, m) is definedby a set of (n+1)(m+1) control points k_(i,j). It maps the unit squareinto a smooth-continuous surface embedded within a space of the samedimensionality as (k_(i,j)). For example, if k are all points in afour-dimensional space, then the surface will be within afour-dimensional space. This relationship holds true for aone-dimensional space, a two-dimensional space, a fifty-dimensionalspace, etc.

A two-dimensional Bézier surface can be defined as a parametric surfacewhere the position of a point p as a function of the parametriccoordinates u, v is given by:

${P\left( {u,v} \right)} = {\sum\limits_{i = 0}^{n}{\sum\limits_{j = 0}^{m}{{B_{i}^{n}(u)}{B_{j}^{m}(v)}k_{i,j}}}}$evaluated over the unit square, where

${B_{i}^{n}(u)} = {\begin{pmatrix}n \\i\end{pmatrix}{u^{i}\left( {1 - u} \right)}^{n - i}}$is a Bernstein polynomial and

$\begin{pmatrix}n \\i\end{pmatrix} = \frac{n!}{{i!}*{\left( {n - i} \right)!}}$is the binomial coefficient. See Grune et al, On Numerical Algorithm andInteractive Visualization for Optimal Control Problems, Journal ofComputation and Visualization in Science, Vol. 1, No. 4, July 1999,which is hereby incorporated by reference in its entirety into thisDetailed Description.

Various other surface rendering techniques are disclosed in otherreferences. For example, see the surface rendering techniques disclosedin the following publications: Lorensen et al., Marching Cubes: A highResolution 3d Surface Construction Algorithm, Computer Graphics, 21-3:163-169, 1987; Farin et al., NURB Curves & Surfaces: From ProjectiveGeometry to Practical Use, Wellesley, 1995; Kumar et al, RobustIncremental Polygon Triangulation for Surface Rendering, WSCG, 2000;Fleischer et al., Accurate Polygon Scan Conversion Using Half-OpenIntervals, Graphics Gems III, p. 362-365, code: p. 599-605, 1992; Foleyet al., Computer Graphics: Principles and Practice, Addison Wesley,1990; Glassner, Principles of Digital Image Synthesis, Morgan Kaufmann,1995, all of which are hereby incorporated by reference in theirentireties into this Detailed Description.

d. Selecting a Jig Blank Most Similar in Size and/or Configuration tothe Size of the Patient's Femur Lower End.

As mentioned above, an arthroplasty jig 2, such as a femoral jig 2Aincludes an interior portion 100 and an exterior portion 102. Thefemoral jig 2A is formed from a femur jig blank 50A, which, in oneembodiment, is selected from a finite number of femur jig blank sizes.The selection of the femur jig blank 50A is based on a comparison of thedimensions of the patient's femur lower end 204 to the dimensions and/orconfigurations of the various sizes of femur jig blanks 50A to selectthe femur jig blank 50A most closely resembling the patient's femurlower end 204 with respect to size and/or configuration. This selectedfemur jig blank 50A has an outer or exterior side or surface 232 thatforms the exterior portion 232 of the femur jig 2A. The 3D surfacecomputer model 40 discussed with respect to the immediately precedingsection of this Detail Description is used to define a 3D surface 40into the interior side 230 of computer model of a femur jig blank 50A.Furthermore, in some embodiments, the overestimation of the proceduredescribed below may be used to adjust the 3D surface model 40.

By selecting a femur jig blank 50A with an exterior portion 232 close insize to the patient's lower femur end 204, the potential for an accuratefit between the interior portion 230 and the patient's femur isincreased. Also, the amount of material that needs to be machined orotherwise removed from the jig blank 50A is reduced, thereby reducingmaterial waste and manufacturing time.

For a discussion of a method of selecting a jig blank 50 most closelycorresponding to the size and/or configuration of the patient's lowerfemur end, reference is first made to FIGS. 3-4B. FIG. 3A is a topperspective view of a left femoral cutting jig blank 50AL havingpredetermined dimensions. FIG. 3B is a bottom perspective view of thejig blank 50AL depicted in FIG. 3A. FIG. 3C is plan view of an exteriorside or portion 232 of the jig blank 50AL depicted in FIG. 3A. FIG. 4Ais a plurality of available sizes of left femur jig blanks 50AL, eachdepicted in the same view as shown in FIG. 3C. FIG. 4B is a plurality ofavailable sizes of right femur jig blanks 50AR, each depicted in thesame view as shown in FIG. 3C.

A common jig blank 50, such as the left jig blank 50AL depicted in FIGS.3A-3C and intended for creation of a left femur jig that can be usedwith a patient's left femur, may include a posterior edge 240, ananterior edge 242, a lateral edge 244, a medial edge 246, a lateralcondyle portion 248, a medial condyle portion 250, the exterior side 232and the interior side 230. The jig blank 50AL of FIGS. 3A-3C may be anyone of a number of left femur jig blanks 50AL available in a limitednumber of standard sizes. For example, the jig blank 50AL of FIGS. 3A-3Cmay be an i-th left femur jig blank, where i=1, 2, 3, 4, . . . m and mrepresents the maximum number of left femur jig blank sizes.

As indicated in FIG. 3C, the anterior-posterior extent JAi of the jigblank 50AL is measured from the anterior edge 242 to the posterior edge240 of the jig blank 50AL. The medial-lateral extent JMi of the jigblank 50AL is measured from the lateral edge 244 to the medial edge 246of the jig blank 50AL.

As can be understood from FIG. 4A, a limited number of left femur jigblank sizes may be available for selection as the left femur jig blanksize to be machined into the left femur cutting jig 2A. For example, inone embodiment, there are nine sizes (m=9) of left femur jig blanks 50ALavailable. As can be understood from FIG. 3C, each femur jig blank 50ALhas an anterior-posterior/medial-lateral aspect ratio defined as JAi toJMi (e.g., “JAi/JMi” aspect ratio). Thus, as can be understood from FIG.4A, jig blank 50AL-1 has an aspect ratio defined as “JA₁/JM₁”, jig blank50AL-2 has an aspect ratio defined as “JA₂/JM₂”, jig blank 50AL-3 has anaspect ratio defined as “JA₃/JM₃”, jig blank 50AL-4 has an aspect ratiodefined as “JA₄/JM₄”, jig blank 50AL-5 has an aspect ratio defined as“JA₅/JM₅”, jig blank 50AL-6 has an aspect ratio defined as “JA₆/JM₆”,jig blank 50AL-7 has an aspect ratio defined as “JA₇/JM₇”, jig blank50AL-8 has an aspect ratio defined as “JA₈/JM₈”, and jig blank 50AL-9has an aspect ratio defined as “JA₉/JM₉”.

The jig blank aspect ratio is utilized to design left femur jigs 2Adimensioned specific to the patient's left femur features. In oneembodiment, the jig blank aspect ratio can be the exterior dimensions ofthe left femur jig 2A. In another embodiment, the jig blank aspect ratiocan apply to the left femur jig fabrication procedure for selecting theleft jig blank 50AL having parameters close to the dimensions of thedesired left femur jig 2A. This embodiment can improve the costefficiency of the left femur jig fabrication process because it reducesthe amount of machining required to create the desired jig 2 from theselected jig blank 50.

In FIG. 4A, the N−1 direction represents increasing jig aspect ratiosmoving from jig 50AL-3 to jig 50AL-2 to jig 50AL-1, where“JA₃/JM₃”<“JA₂/JM₂”<“JA₁/JM₁”. The increasing ratios of the jigs 50ALrepresent the corresponding increment of JAi values, where the jigs' JMivalues remain the same. In other words, since JA₃<JA₂<JA₁, andJM₃=JM₂=JM₁, then “JA₃/JM₃”<“JA₂/JM₂”<“JA₁/JM₁”. One example of theincrement level can be an increase from 5% to 20%.

The same rationale applies to the N-2 direction and the N-3 direction.For example, the N-2 direction represents increasing jig aspect ratiosfrom jig 50AL-6 to jig 50AL-5 to jig 50AL-4, where“JA₄/JM₄”<“JA₅/JM₅”<“JA₆/JM₆”. The increasing ratios of the jigs 50ALrepresent the corresponding increment of JAi values, where the JMivalues remain the same. The N-3 direction represents increasing jigaspect ratios from jig 50AL-9 to jig 50AL-8 to jig 50AL-7, where“JA₇/JM₇”<“JA₈/JM₈”<“JA₉/JM₉”. The increasing ratios of the jigs 50ALrepresent the corresponding increment of JAi values, where the JMivalues remain the same.

As can be understood from the plot 300 depicted in FIG. 7 and discussedlater in this Detailed Discussion, the E-1 direction corresponds to thesloped line joining Group 1, Group 4 and Group 7. Similarly, the E-2direction corresponds to the sloped line joining Group 2, Group 5 andGroup 8. Also, the E-3 direction corresponds to the sloped line joiningGroup 3, Group 6 and Group 9.

As indicated in FIG. 4A, along direction E-2, the jig aspect ratiosremain the same among jigs 50AL-2, 50AL-5 and jig 50AL-8, where“JA₂/JM₂”=“JA₅/JM₅”=“JA₈/JM₈”. However, comparing to jig 50AL-2, jig50AL-5 is dimensioned larger and longer than jig 50AL-2. This is becausethe JA₅ value for jig 50AL-5 increases proportionally with the incrementof its JM₅ value in certain degrees in all X, Y, and Z-axis directions.In a similar fashion, jig 50AL-8 is dimensioned larger and longer thanjig 50AL-5 because the JA₈ increases proportionally with the incrementof its JM₈ value in certain degrees in all X, Y, and Z-axis directions.One example of the increment can be an increase from 5% to 20%.

The same rationale applies to directions E-1 and E-3. For example, inE-3 direction the jig ratios remain the same among the jigs 50AL-3,50AL-6 and jig 50AL-9. Compared to jig 50AL-3, jig 50AL-6 is dimensionedbigger and longer because both JM₆ and JA₆ values of jig 50AL-6 increaseproportionally in all X, Y, and Z-axis directions. Compared to jig50AL-6, jig 50AL-9 is dimensioned bigger and longer because both JM₉ andJA₉ values of jig 50AL-9 increase proportionally in all X, Y, andZ-axis.

As can be understood from FIG. 4B, a limited number of right femur jigblank sizes may be available for selection as the right femur jig blanksize to be machined into the right femur cutting jig 2A. For example, inone embodiment, there are nine sizes (m=9) of right femur jig blanks50AR available. As can be understood from FIG. 3, each femur jig blank50AR has an anterior-posterior/medial-lateral aspect ratio defined asJAi to JMi (e.g., “JAi/JMi” aspect ratio). Thus, as can be understoodfrom FIG. 4B, jig blank 50AR-1 has an aspect ratio defined as “JA₁/JM₁”,jig blank 50AR-2 has an aspect ratio defined as “JA₂/JM₂”, jig blank50AR-3 has an aspect ratio defined as “JA₃/JM₃”, jig blank 50AR-4 has anaspect ratio defined as “JA₄/JM₄”, jig blank 50AR-5 has an aspect ratiodefined as “JA₅/JM₅”, jig blank 50AR-6 has an aspect ratio defined as“JA₆/JM₆”, jig blank 50AR-7 has an aspect ratio defined as “JA₇/JM₇”,jig blank 50AR-8 has an aspect ratio defined as “JA₈/JM₈”, and jig blank50AR-9 has an aspect ratio defined as “JA₉/JM₉”.

The jig blank aspect ratio may be utilized to design right femur jigs 2Adimensioned specific to the patient's right femur features. In oneembodiment, the jig blank aspect ratio can be the exterior dimensions ofthe right femur jig 2A. In another embodiment, the jig blank aspectratio can apply to the right femur jig fabrication procedure forselecting the right jig blank 50AR having parameters close to thedimensions of the desired right femur jig 2A. This embodiment canimprove the cost efficiency of the right femur jig fabrication processbecause it reduces the amount of machining required to create thedesired jig 2 from the selected jig blank 50.

In FIG. 4B, the N−1 direction represents increasing jig aspect ratiosmoving from jig 50AR-3 to jig 50AR-2 to jig 50AR-1, where“JA₃/JM₃”<“JA₂/JM₂”<“JA₁/JM₁”. The increasing ratios of the jigs 50ARrepresent the corresponding increment of JAi values, where the jigs' JMivalues remain the same. In other words, since JA₃<JA₂<JA₁, andJM₃=JM₂=JM₁, then “JA₃/JM₃”<“JA₂/JM₂”<“JA₁/JM₁”. One example of theincrement level can be an increase from 5% to 20%.

The same rationale applies to the N-2 direction and the N-3 direction.For example, the N-2 direction represents increasing jig aspect ratiosfrom jig 50AR-6 to jig 50AR-5 to jig 50AR-4, where“JA₄/JM₄”<“JA₅/JM₅”<“JA₆/JM₆”. The increasing ratios of the jigs 50ARrepresent the corresponding increment of JAi values, where the JMivalues remain the same. The N-3 direction represents increasing jigaspect ratios from jig 50AR-9 to jig 50AR-8 to jig 50AR-7, where“JA₇/JM₇”<“JA₈/JM₈”<“JA₉/JM₉”. The increasing ratios of the jigs 50ARrepresent the corresponding increment of JAi values, where the JMivalues remain the same.

As indicated in FIG. 4B, along direction E-2, the jig aspect ratiosremain the same among jigs 50AR-2, 50AR-5 and jig 50AR-8, where“JA₂/JM₂”=“JA₅/JM₅”=“JA₈/JM₈”. However, comparing to jig 50AR-2, jig50AR-5 is dimensioned larger and longer than jig 50AR-2. This is becausethe JA₅ value for jig 50AR-5 increases proportionally with the incrementof its JM₅ value in certain degrees in all X, Y, and Z-axis directions.In a similar fashion, jig 50AR-8 is dimensioned larger and longer thanjig 50AR-5 because the JA₈ increases proportionally with the incrementof its JM₈ value in certain degrees in all X, Y, and Z-axis directions.One example of the increment can be an increase from 5% to 20%.

The same rationale applies to directions E-1 and E-3. For example, inE-3 direction the jig ratios remain the same among the jigs 50AR-3,50AR-6 and jig 50AR-9. Compared to jig 50AR-3, jig 50AR-6 is dimensionedbigger and longer because both JM₆ and JA₆ values of jig 50AR-6 increaseproportionally in all X, Y, and Z-axis directions. Compared to jig50AR-6, jig 50AR-9 is dimensioned bigger and longer because both JM₉ andJA₉ values of jig 50AR-9 increase proportionally in all X, Y, andZ-axis.

The dimensions of the lower or knee joint forming end 204 of thepatient's femur 18 can be determined by analyzing the 3D surface model40 or 3D arthritic model 36 in a manner similar to those discussed withrespect to the jig blanks 50. For example, as depicted in FIG. 5, whichis an axial view of the 3D surface model 40 or arthritic model 36 of thepatient's left femur 18 as viewed in a direction extending distal toproximal, the lower end 204 of the surface model 40 or arthritic model36 may include an anterior edge 262, a posterior edge 260, a medial edge264, a lateral edge 266, a medial condyle 268, and a lateral condyle270. The femur dimensions may be determined for the bottom end face ortibia articulating surface 204 of the patient's femur 18 via analyzingthe 3D surface model 40 of the 3D arthritic model 36. These femurdimensions can then be utilized to configure femur jig dimensions andselect an appropriate femur jig.

As shown in FIG. 5, the anterior-posterior extent fAP of the lower end204 of the patient's femur 18 (i.e., the lower end 204 of the surfacemodel 40 of the arthritic model 36, whether formed via open orclosed-loop analysis) is the length measured from the anterior edge 262of the femoral lateral groove to the posterior edge 260 of the femorallateral condyle 270. The medial-lateral extent fML of the lower end 204of the patient's femur 18 is the length measured from the medial edge264 of the medial condyle 268 to the lateral edge 266 of the lateralcondyle 270.

In one embodiment, the anterior-posterior extent fAP and medial-lateralextent fML of the femur lower end 204 can be used for an aspect ratiofAP/fML of the femur lower end. The aspect ratios fAP/fML of a largenumber (e.g., hundreds, thousands, tens of thousands, etc.) of patientknees can be compiled and statistically analyzed to determine the mostcommon aspect ratios for jig blanks that would accommodate the greatestnumber of patient knees. This information may then be used to determinewhich one, two, three, etc. aspect ratios would be most likely toaccommodate the greatest number of patient knees.

The system 4 analyzes the lower ends 204 of the patient's femur 18 asprovided via the surface model 40 of the arthritic model 36 (whether thearthritic model 36 is an 3D surface model generated via an open-loop ora 3D volumetric solid model generated via a closed-loop process) toobtain data regarding anterior-posterior extent fAP and medial-lateralextent fML of the femur lower ends 204. As can be understood from FIG.6, which depicts the selected model jig blank 50AL of FIG. 3Csuperimposed on the model femur lower end 204 of FIG. 5, the femurdimensional extents fAP, fML are compared to the jig blank dimensionalextents jAP, jML to determine which jig blank model to select as thestarting point for the machining process and the exterior surface modelfor the jig model.

As shown in FIG. 6, a prospective left femoral jig blank 50AL issuperimposed to mate with the left femur lower end 204 of the patient'sanatomical model as represented by the surface model 40 or arthriticmodel 36. The jig blank 50AL covers most of medial condyle 268 and thelateral condyle 270, leaving small exposed condyle regions including t1,t2, t3. The medial medial-lateral condyle region t1 represents theregion between the medial edge 264 of the medial condyle 268 and themedial edge 246 of the jig blank 50AL. The lateral medial-lateralcondyle region t2 represents the region between the lateral edge 266 ofthe lateral condyle 270 and the lateral edge 244 of the jig blank 50AL.The posterior anterior-posterior region t3 represents the condyle regionbetween the posterior edge 260 of the lateral condyle 270 and theposterior edge 240 of the jig blank 50AL.

The anterior edge 242 of the jig blank 50AL extends past the anterioredge 262 of the left femur lower end 204 as indicated by anterioranterior-posterior overhang t4. Specifically, the anterioranterior-posterior overhang t4 represents the region between theanterior edge 262 of the lateral groove of femur lower end 204 and theanterior edge 242 of the jig blank 50AL. By obtaining and employing thefemur anterior-posterior fAP data and the femur medial-lateral fML data,the system 4 can size the femoral jig blank 50AL according to thefollowing formulas: as jFML=fML−t1−t2 and jFAP=fAP−t3+t4, wherein jFMLis the medial-lateral extent of the femur jig blank 50AL and jFAP is theanterior-posterior extent of the femur jig blank 50AL. In oneembodiment, t1, t2, t3 and t4 will have the following ranges: 2 mm≦t1≦6mm; 2 mm≦t2≦6 mm; 2 mm≦t3≦12 mm; and 15 mm≦t4≦25 mm. In anotherembodiment, t1, t2, t3 and t4 will have the following values: t1=3 mm;t2=3 mm; t3=6 mm; and t4=20 mm.

FIG. 7A is an example scatter plot 300 for selecting from a plurality ofcandidate jig blanks sizes a jig blank size appropriate for the lowerend 204 of the patient's femur 18. In one embodiment, the X-axisrepresents the patient's femoral medial-lateral length fML inmillimeters, and the Y-axis represents the patient's femoralanterior-posterior length fAP in millimeters. In one embodiment, theplot is divided into a number of jig blank size groups, where each groupencompasses a region of the plot 300 and is associated with specificparameters JM_(r), JA_(r) of a specific candidate jig blank size.

In one embodiment, the example scatter plot 300 depicted in FIG. 7A hasnine jig blank size groups, each group pertaining to a single candidatejig blank size. However, depending on the embodiment, a scatter plot 300may have a greater or lesser number of jig blank size groups. The higherthe number of jig blank size groups, the higher the number of thecandidate jig blank sizes and the more dimension specific a selectedcandidate jig blank size will be to the patient's knee features and theresulting jig 2. The more dimension specific the selected candidate jigblank size, the lower the amount of machining required to produce thedesired jig 2 from the selected jig blank 50.

Conversely, the lower the number of jig blank size groups, the lower thenumber of candidate jig blank sizes and the less dimension specific aselected candidate jig blank size will be to the patient's knee featuresand the resulting jig 2. The less dimension specific the selectedcandidate jig blank size, the higher the amount of machining required toproduce the desired jig 2 from the selected jig blank 50, adding extraroughing during the jig fabrication procedure.

As can be understood from FIG. 7A, in one embodiment, the nine jig blanksize groups of the plot 300 have the parameters JM_(r), JA_(r) asfollows. Group 1 has parameters JM₁, JA₁. JM₁ represents themedial-lateral extent of the first femoral jig blank size, whereinJM₁=70 mm. JA₁ represents the anterior-posterior extent of the firstfemoral jig blank size, wherein JA₁=70.5 mm. Group 1 covers thepatient's femur fML and fAP data wherein 55 mm<fML<70 mm and 61mm<fAP<70.5 mm.

Group 2 has parameters JM₂, JA₂. JM₂ represents the medial-lateralextent of the second femoral jig blank size, wherein JM₂=70 mm. JA₂represents the anterior-posterior extent of the second femoral jig blanksize, wherein JA₂=61.5 mm. Group 2 covers the patient's femur fML andfAP data wherein 55 mm<fML<70 mm and 52 mm<fAP<61.5 mm.

Group 3 has parameters JM₃, JA₃. JM₃ represents the medial-lateralextent of the third femoral jig blank size, wherein JM₃=70 mm. JA₃represents the anterior-posterior extent of the third femoral jig blanksize, wherein JA₃=52 mm. Group 3 covers the patient's femur fML and fAPdata wherein 55 mm<fML<70 mm and 40 mm<fAP<52 mm.

Group 4 has parameters JM₄, JA₄. JM₄ represents the medial-lateralextent of the fourth femoral jig blank size, wherein JM₄=85 mm. JA₄represents the anterior-posterior extent of the fourth femoral jig blanksize, wherein JA₄=72.5 mm. Group 4 covers the patient's femur fML andfAP data wherein 70 mm<fML<85 mm and 63.5 mm<fAP<72.5 mm.

Group 5 has parameters JM₅, JA₅. JM₅ represents the medial-lateralextent of the fifth femoral jig blank size, wherein JM₅=85 mm. JA₅represents the anterior-posterior extent of the fifth femoral jig blanksize, wherein JA₅=63.5 mm. Group 5 covers the patient's femur fML andfAP data wherein 70 mm<fML<85 mm and 55 mm<fAP<63.5 mm.

Group 6 has parameters JM₆, JA₆. JM₆ represents the medial-lateralextent of the sixth femoral jig blank size, wherein JM₆=85 mm. JA₆represents the anterior-posterior extent of the sixth femoral jig blanksize, wherein JA₆=55 mm. Group 6 covers the patient's femur fML and fAPdata wherein 70 mm<fML<85 mm and 40 mm<fAP<55 mm.

Group 7 has parameters JM₇, JA₇. JM₇ represents the medial-lateralextent of the seventh femoral jig blank size, wherein JM₇=100 mm. JA₇represents the anterior-posterior extent of the seventh femoral jigblank size, wherein JA₇=75 mm. Group 7 covers the patient's femur fMLand fAP data wherein 85 mm<fML<100 mm and 65 mm<fAP<75 mm.

Group 8 has parameters JM₈, JA₈. JM₈ represents the medial-lateralextent of the eighth femoral jig blank size, wherein JM₈=100 mm. JA₈represents the anterior-posterior extent of the eighth femoral jig blanksize, wherein JA₈=65 mm. Group 8 covers the patient's femur fML and fAPdata wherein 85 mm<fML<100 mm and 57.5 mm<fAP<65 mm.

Group 9 has parameters JM₉, JA₉. JM₉ represents the medial-lateralextent of the ninth femoral jig blank size, wherein JM₉=100 mm. JA₉represents the anterior-posterior extent of the ninth femoral jig blanksize, wherein JA₉=57.5 mm. Group 9 covers the patient's femur fML andfAP data wherein 85 mm<fML<100 mm and 40 mm<fAP<57.5 mm.

As can be understood from FIG. 7B, which is a flow diagram illustratingan embodiment of a process of selecting an appropriately sized jigblank, bone anterior-posterior and medial-lateral extents fAP, fML aredetermined for the lower end 204 of the surface model 40 of thearthritic model 36 [block 2000]. The bone extents fAP, fML of the lowerend 204 are mathematically modified according to the above discussedjFML and jFAP formulas to arrive at the minimum femur jig blankanterior-posterior extent jFAP and medial-lateral extent jFML [block2010]. The mathematically modified bone extents fAP, fML or, morespecifically, the minimum femur jig blank anterior-posterior andmedial-lateral extents jFAP, jFML are referenced against the jig blankdimensions in the plot 300 of FIG. 7A [block 2020]. The plot 300 maygraphically represent the extents of candidate femur jig blanks forminga jig blank library. The femur jig blank 50A is selected to be the jigblank size having the smallest extents that are still sufficiently largeto accommodate the minimum femur jig blank anterior-posterior andmedial-lateral extents JFAP, jFML [block 2030].

In one embodiment, the exterior of the selected jig blank size is usedfor the exterior surface model of the jig model, as discussed below. Inone embodiment, the selected jig blank size corresponds to an actual jigblank that is placed in the CNC machine and milled down to the minimumfemur jig blank anterior-posterior and medial-lateral extents jFAP, jFMLto machine or otherwise form the exterior surface of the femur jig 2A.

The method outlined in FIG. 7B and in reference to the plot 300 of FIG.7A can be further understood from the following example. As measured inFIG. 6 with respect to the lower end 204 of the patient's femur 18, theextents of the patient's femur are as follows: fML=79.2 mm and fAP=54.5mm [block 2000]. As previously mentioned, the lower end 204 may be partof the surface model 40 of the arthritic model 36. Once the fML and fAPmeasurements are determined from the lower end 204, the correspondingjig jFML data and jig jFAP data can be determined via theabove-described jFML and jFAP formulas: jFML=fML−t1−t2, wherein t1=3 mmand t2=3 mm; and jFAP=fAP−t3+t4, wherein t3=6 mm and t4=20 mm [block2010]. The result of the jFML and jFAP formulas is jFML=73.2 mm andjFAP=68.5 mm.

As can be understood from the plot 300 of FIG. 7, the determined jigdata (i.e., jFML=73.2 mm and jFAP=68.5 mm) falls in Group 4 of the plot300. Group 4 has the predetermined femur jig blank parameters (JM₄, JA₄)of JM₄=85 mm and JA₄=72.5 mm. These predetermined femur jig blankparameters are the smallest of the various groups that are stillsufficiently large to meet the minimum femur blank extents jFAP, jFML[block 2020]. These predetermined femur jig blank parameters (JM₄=85 mmand JA₄=72.5 mm) may be selected as the appropriate femur jig blank size[block 2030].

In one embodiment, the predetermined femur jig blank parameters (85 mm,72.5 mm) can apply to the femur exterior jig dimensions as shown in FIG.3C. In other words, the jig blank exterior is used for the jig modelexterior as discussed with respect to FIGS. 8A-9C. Thus, the exterior ofthe femur jig blank 50A undergoes no machining, and the unmodifiedexterior of the jig blank 50A with its predetermined jig blankparameters (85 mm, 72.5 mm) serves as the exterior of the finished femurjig 2A.

In another embodiment, the femur jig blank parameters (85 mm, 72.5 mm)can be selected for jig fabrication in the machining process. Thus, afemur jig blank 50A having predetermined parameters (85 mm, 72.5 mm) isprovided to the machining process such that the exterior of the femurjig blank 50A will be machined from its predetermined parameters (85 mm,72.5 mm) down to the desired femur jig parameters (73.2, 68.5 mm) tocreate the finished exterior of the femur jig 2A. As the predeterminedparameters (85 mm, 72.5 mm) are selected to be relatively close to thedesired femur jig parameters (73.2, 68.5 mm), machining time andmaterial waste are reduced.

While it may be advantageous to employ the above-described jig blankselection method to minimize material waste and machining time, in someembodiments, a jig blank will simply be provided that is sufficientlylarge to be applicable to all patient bone extents fAP, fML. Such a jigblank is then machined down to the desired jig blank extents jFAP, jFML,which serve as the exterior surface of the finished jig 2A.

In one embodiment, the number of candidate jig blank size groupsrepresented in the plot 300 is a function of the number of jig blanksizes offered by a jig blank manufacturer. For example, a first plot 300may pertain only to jig blanks manufactured by company A, which offersnine jig blank sizes. Accordingly, the plot 300 has nine jig blank sizegroups. A second plot 300 may pertain only to jig blanks manufactured bycompany B, which offers twelve jig blank size groups. Accordingly, thesecond plot 300 has twelve jig blank size groups.

A plurality of candidate jig blank sizes exist, for example, in a jigblank library as represented by the plot 300 of FIG. 7B. While eachcandidate jig blank may have a unique combination of anterior-posteriorand medial-lateral dimension sizes, in some embodiments, two or more ofthe candidate jig blanks may share a common aspect ratio jAP/jML orconfiguration. The candidate jig blanks of the library may be groupedalong sloped lines of the plot 300 according to their aspect ratiosjAP/jML.

In one embodiment, the jig blank aspect ratio jAP/jML may be used totake a workable jig blank configuration and size it up or down to fitlarger or smaller individuals.

As can be understood from FIG. 7A, a series of 98 OA patients havingknee disorders were entered into the plot 300 as part of a femur jigdesign study. Each patient's femur fAP and fML data was measured andmodified via the above-described jFML and jFAP formulas to arrive at thepatient's jig blank data (jFML, jFAP). The patient's jig blank data wasthen entered into the plot 300 as a point. As can be understood fromFIG. 7A, no patient point lies outside the parameters of an availablegroup. Such a process can be used to establish group parameters and thenumber of needed groups.

In one embodiment, the selected jig blank parameters can be the femoraljig exterior dimensions that are specific to patient's knee features. Inanother embodiment, the selected jig blank parameters can be chosenduring fabrication process.

e. Formation of 3D Femoral Jig Model.

For a discussion of an embodiment of a method of generating a 3D femurjig model 346 generally corresponding to the “integrated jig data” 48discussed with respect to [block 150] of FIG. 1E, reference is made toFIGS. 3A-3C, FIGS. 8A-8B, FIGS. 9A-9C and FIG. 10A-10B. FIGS. 3A-3C arevarious views of a femur jig blank 50A. FIGS. 8A-8B are, respectively,exterior and interior perspective views of a femur jig blank exteriorsurface model 232M. FIGS. 9A and 9B are exterior perspective views ofthe jig blank exterior model 232M and bone surface model 40 beingcombined, and FIG. 9C is a cross section through the combined models232M, 40 as taken along section line 9C-9C in FIG. 9B. FIGS. 10A and 10Bare, respectively, exterior and interior perspective views of theresulting femur jig model 346 after having “saw cut and drill hole data”44 integrated into the jig model 346 to become an integrated or completejig model 348 generally corresponding to the “integrated jig data” 48discussed with respect to [block 150] of FIG. 1E.

As can be understood from FIGS. 3A-3C, the jig blank 50A, which hasselected predetermined dimensions as discussed with respect to FIG. 7,includes an interior surface 230 and an exterior surface 232. Theexterior surface model 232M depicted in FIGS. 8A and 8B is extracted orotherwise created from the exterior surface 232 of the jig blank model50A. Thus, the exterior surface model 232M is based on the jig blankaspect ratio of the femur jig blank 50A selected as discussed withrespect to FIG. 7 and is dimensioned specific to the patient's kneefeatures. The femoral jig surface model 232M can be extracted orotherwise generated from the jig blank model 50A of FIGS. 3A-3C byemploying any of the computer surface rendering techniques describedabove.

As can be understood from FIGS. 9A-9C, the exterior surface model 232Mis combined with the femur surface model 40 to respectively form theexterior and interior surfaces of the femur jig model 346. The femursurface model 40 represents the interior or mating surface of the femurjig 2A and corresponds to the femur arthroplasty target area 42. Thus,the model 40 allows the resulting femur jig 2A to be indexed to thearthroplasty target area 42 of the patient's femur 18 such that theresulting femur jig 2A will matingly receive the arthroplasty targetarea 42 during the arthroplasty procedure. The two surface models 232M,40 combine to provide a patient-specific jig model 346 for manufacturingthe femur jig 2A. In some embodiments, this patient-specific jig model346 may include one or more areas of overestimation (as described below)to accommodate for irregularities in the patient's bone surface and/orlimitations in jig manufacturing capabilities.

As can be understood from FIGS. 9B and 9C, once the models 232M, 40 areproperly aligned, a gap will exist between the two models 232M, 40. Animage sewing method or image sewing tool is applied to the alignedmodels 232M, 40 to join the two surface models together to form the 3Dcomputer generated jig model 346 of FIG. 9B into a single-piece,joined-together, and filled-in jig model 346 similar in appearance tothe integrated jig model 348 depicted in FIGS. 10A and 10B. In oneembodiment, the jig model 346 may generally correspond to thedescription of the “jig data” 46 discussed with respect [block 145] ofFIG. 1E.

As can be understood from FIGS. 9B and 9C, the geometric gaps betweenthe two models 232M, 40, some of which are discussed below with respectto thicknesses P₁, P₂ and P₃, may provide certain space between the twosurface models 232M, 40 for slot width and length and drill bit lengthfor receiving and guiding cutting tools during TKA surgery. Because theresulting femur jig model 348 depicted in FIGS. 10A and 10B may be a 3Dvolumetric model generated from 3D surface models 232M, 40, a space orgap should be established between the 3D surface models 232M, 40. Thisallows the resulting 3D volumetric jig model 348 to be used to generatean actual physical 3D volumetric femur jig 2.

In some embodiments, the image processing procedure may include a modelrepair procedure for repairing the jig model 346 after alignment of thetwo models 232M, 40. For example, various methods of the model repairinginclude, but are not limit to, user-guided repair, crack identificationand filling, and creating manifold connectivity, as described in:Nooruddin et al., Simplification and Repair of Polygonal Models UsingVolumetric Techniques (IEEE Transactions on Visualization and ComputerGraphics, Vol. 9, No. 2, April-June 2003); C. Erikson, Error Correctionof a Large Architectural Model: The Henderson County Courthouse(Technical Report TR95-013, Dept. of Computer Science, Univ. of NorthCarolina at Chapel Hill, 1995); D. Khorramabdi, A Walk through thePlanned CS Building (Technical Report UCB/CSD 91/652, Computer ScienceDept., Univ. of California at Berkeley, 1991); Morvan et al., IVECS: AnInteractive Virtual Environment for the Correction of .STL files (Proc.Conf. Virtual Design, August 1996); Bohn et al., A Topology-BasedApproach for Shell-Closure, Geometric Modeling for Product Realization,(P. R. Wilson et al., pp. 297-319, North-Holland, 1993); Barequet etal., Filling Gaps in the Boundary of a Polyhedron, Computer AidedGeometric Design (vol. 12, no. 2, pp. 207-229, 1995); Barequet et al.,Repairing CAD Models (Proc. IEEE Visualization '97, pp. 363-370, October1997); and Gueziec et al., Converting Sets of Polygons to ManifoldSurfaces by Cutting and Stitching, (Proc. IEEE Visualization 1998, pp.383-390, October 1998). Each of these references is incorporated intothis Detailed Description in their entireties.

As can be understood from FIGS. 10A and 10B, the integrated jig model348 may include several features based on the surgeon's needs. Forexample, the jig model 348 may include a slot feature 30 for receivingand guiding a bone saw and drill holes 32 for receiving and guiding bonedrill bits. As can be understood from FIGS. 9B and 9C, to providesufficient structural integrity to allow the resulting femur jig 2A tonot buckle or deform during the arthroplasty procedure and to adequatelysupport and guide the bone saw and drill bits, the gap 350 between themodels 232M, 40 may have the following offsets P₁, P₂, and P₃.

As can be understood from FIGS. 9B-10B, in one embodiment, thickness P₁extends along the length of the anterior drill holes 32A between themodels 232M, 40 and is for supporting and guiding a bone drill receivedtherein during the arthroplasty procedure. Thickness P₁ may be at leastapproximately four millimeters or at least approximately fivemillimeters thick. The diameter of the anterior drill holes 32A may beconfigured to receive a cutting tool of at least one-third inches.

Thickness P₂ extends along the length of a saw slot 30 between themodels 232M, 40 and is for supporting and guiding a bone saw receivedtherein during the arthroplasty procedure. Thickness P₂ may be at leastapproximately 10 mm or at least 15 mm thick.

Thickness P₃ extends along the length of the posterior drill holes 32Pbetween the models 232M, 40 and is for supporting and guiding a bonedrill received therein during the arthroplasty procedure. Thickness P₃may be at least approximately five millimeters or at least eightmillimeters thick. The diameter of the drill holes 32 may be configuredto receive a cutting tool of at least one-third inches.

In addition to providing sufficiently long surfaces for guiding drillbits or saws received therein, the various thicknesses P₁, P₂, P₃ arestructurally designed to enable the femur jig 2A to bear vigorous femurcutting, drilling and reaming procedures during the TKR surgery.

As indicated in FIGS. 10A and 10B, the integrated jig model 348 mayinclude: feature 400 that matches the patient's distal portion of themedial condyle cartilage; feature 402 that matches the patient's distalportion of the lateral condyle cartilage; projection 404 that can beconfigured as a contact or a hook and may securely engage the resultingjig 2A onto the patient's anterior femoral joint surface during the TKRsurgery; and the flat surface 406 that provides a blanked labeling areafor listing information regarding the patient, surgeon or/and thesurgical procedure. Also, as discussed above, the integrated jig model348 may include the saw cut slot 30 and the drill holes 32. The innerportion or side 100 of the jig model 348 (and the resulting femur jig2A) is the femur surface model 40, which will matingly receive thearthroplasty target area 42 of the patient's femur 18 during thearthroplasty procedure. In some embodiments, the overestimation of theprocedure described below may be used to adjust the 3D surface model 40.

As can be understood by referring to [block 105] of FIG. 1B and FIGS.2A-2F, in one embodiment when cumulating the image scans 16 to generatethe one or the other of the models 40, 22, the models 40, 22 arereferenced to point P, which may be a single point or a series ofpoints, etc. to reference and orient the models 40, 22 relative to themodels 22, 28 discussed with respect to FIG. 1C and utilized for POP.Any changes reflected in the models 22, 28 with respect to point P(e.g., point P becoming point P′) on account of the POP is reflected inthe point P associated with the models 40, 22 (see [block 135] of FIG.1D). Thus, as can be understood from [block 140] of FIG. 1D and FIGS.9A-9C, when the jig blank exterior surface model 232M is combined withthe surface model 40 (or a surface model developed from the arthriticmodel 22) to create the jig model 346, the jig model 346 is referencedand oriented relative to point P′ and is generally equivalent to the“jig data” 46 discussed with respect to [block 145] of FIG. 1E.

Because the jig model 346 is properly referenced and oriented relativeto point P′, the “saw cut and drill hole data” 44 discussed with respectto [block 125] of FIG. 1E can be properly integrated into the jig model346 to arrive at the integrated jig model 348 depicted in FIGS. 10A-10B.The integrated jig model 348 includes the saw cuts 30, drill holes 32and the surface model 40. Thus, the integrated jig model 348 isgenerally equivalent to the “integrated jig data” 48 discussed withrespect to [block 150] of FIG. 1E.

As can be understood from FIG. 11, which illustrates a perspective viewof the integrated jig model 348 mating with the “arthritic model” 22,the interior surface 40 of the jig model 348 matingly receives thearthroplasty target area 42 of the femur lower end 204 such that the jigmodel 348 is indexed to mate with the area 42. (In some embodiments, theinterior surface 40 includes areas of overestimation, described below,to accommodate for irregularities in the patient's bone surface.)Because of the referencing and orientation of the various modelsrelative to the points P, P′ throughout the procedure, the saw cut slot30 and drill holes 32 are properly oriented to result in saw cuts anddrill holes that allow a resulting femur jig 2A to restore a patient'sjoint to a pre-degenerated or natural alignment condition.

As indicated in FIG. 11, the integrated jig model 348 may include a jigbody 500, a projection 502 on one side, and two projections 504, 506 theother side of jig body 500. The projections 504, 506 match the medialand lateral condyle cartilage. The projections 502, 504, 506 extendintegrally from the two opposite ends of the jig body 500.

As can be understood from [blocks 155-165] of FIG. 1E, the integratedjig 348 or, more specifically, the integrated jig data 48 can be sent tothe CNC machine 10 to machine the femur jig 2A from the selected jigblank 50A. For example, the integrated jig data 48 may be used toproduce a production file that provides automated jig fabricationinstructions to a rapid production machine 10, as described in thevarious Park patent applications referenced above. The rapid productionmachine 10 then fabricates the patient-specific arthroplasty femur jig2A from the femur jig blank 50A according to the instructions.

The resulting femur jig 2A may have the features of the integrated jigmodel 348. Thus, as can be understood from FIG. 11, the resulting femurjig 2A may have the slot 30 and the drilling holes 32 formed on theprojections 502, 504, 506, depending on the needs of the surgeon. Thedrilling holes 32 are configured to prevent the possible IR/ER(internal/external) rotational axis misalignment between the femoralcutting jig 2A and the patient's damaged joint surface during the distalfemur cut portion of the TKR procedure. The slot 30 is configured toaccept a cutting instrument, such as a reciprocating slaw blade fortransversely cutting during the distal femur cut portion of the TKR.

f. Defining a 3D Surface Model of an Arthroplasty Target Area of a TibiaUpper End for Use as a Surface of an Interior Portion of a TibiaArthroplasty Cutting Jig.

For a discussion of a method of generating a 3D model 40 of a targetarea 42 of a damaged upper end 604 of a patient's tibia 20, reference ismade to FIGS. 12A-12C. FIG. 12A is an anterior-posterior (“AP”) imageslice 608 of the damaged upper or knee joint end 604 of the patient'stibia 20, wherein the image slice 608 includes an open-loop contour linesegment 610 corresponding to the target area 42 of the damaged upper end604. FIG. 12B is a plurality of image slices (16-1, 16-1, 16-2, . . .16-n) with their respective open-loop contour line segments (610-1,610-2, . . . 610-n), the open-loop contour line segments 610 beingaccumulated to generate the 3D model 40 of the target area 42. FIG. 12Cis a 3D model 40 of the target area 42 of the damaged upper end 604 asgenerated using the open-loop contour line segments (16-1, 16-2, . . .16-n) depicted in FIG. 12B.

As can be understood from FIGS. 1A, 1B and 12A, the imager 8 is used togenerate a 2D image slice 16 of the damaged upper or knee joint end 604of the patient's tibia 20. As depicted in FIG. 12A, the 2D image 16 maybe an AP view of the tibia 20. Depending on whether the imager 8 is aMRI or CT imager, the image slice 16 will be a MRI or CT slice. Thedamaged upper end 604 includes the tibia plateau 612, an anterior tibiashaft surface 614, and an area of interest or targeted area 42 thatextends along the tibia meniscus starting from a portion of the lateraltibia plateau surface to the anterior tibia surface 614. The targetedarea 42 of the tibia upper end may be the articulating contact surfacesof the tibia upper end that contact corresponding articulating contactsurfaces of the femur lower or knee joint end.

As shown in FIG. 12A, the image slice 16 may depict the cancellous bone616, the cortical bone 618 surrounding the cancellous bone, and thearticular cartilage lining portions of the cortical bone 618. Thecontour line 610 may extend along the targeted area 42 and immediatelyadjacent the cortical bone and cartilage to outline the contour of thetargeted area 42 of the tibia upper end 604. The contour line 610extends along the targeted area 42 starting at point C on the lateral ormedial tibia plateau 612 (depending on whether the slice 16 extendsthrough the lateral or medial portion of the tibia) and ends at point Don the anterior tibia shaft surface 614.

In one embodiment, as indicated in FIG. 12A, the contour line 610extends along the targeted area 42, but not along the rest of thesurface of the tibia upper end 604. As a result, the contour line 610forms an open-loop that, as will be discussed with respect to FIGS. 12Band 12C, can be used to form an open-loop region or 3D computer model40, which is discussed with respect to [block 140] of FIG. 1D andclosely matches the 3D surface of the targeted area 42 of the tibiaupper end. (In some embodiments, the 3D model 40 may be deliberatelyconfigured to be larger than the bone surface, in one or more areas, toaccommodate for irregularities. See description below in the context ofoverestimating the tibial mating surface.) Thus, in one embodiment, thecontour line is an open-loop and does not outline the entire corticalbone surface of the tibia upper end 604. Also, in one embodiment, theopen-loop process is used to form from the 2D images 16 a 3D surfacemodel 36 that generally takes the place of the arthritic model 36discussed with respect to [blocks 125-140] of FIG. 1D and which is usedto create the surface model 40 used in the creation of the “jig data” 46discussed with respect to [blocks 145-150] of FIG. 1E.

In one embodiment and in contrast to the open-loop contour line 610depicted in FIGS. 12A and 12B, the contour line is a closed-loop contourline generally the same as the closed-loop contour line 210′ discussedwith respect to FIGS. 2D-2E, except the closed-loop contour linepertains to a tibia instead of a femur. Like the femur closed-loopcontour line discussed with respect to FIG. 2D, a tibia closed-loopcontour line may outline the entire cortical bone surface of the tibiaupper end and results in a closed-loop area. The tibia closed-loopcontour lines are combined in a manner similar that discussed withrespect to the femur contour lines in FIG. 2E. As a result, the tibiaclosed-loop area may require the analysis of the entire surface regionof the tibia upper end 604 and result in the formation of a 3D model ofthe entire tibia upper end 604 in a manner similar to the femur lowerend 204 illustrated in FIG. 2F. Thus, the 3D surface model resultingfrom the tibia closed-loop process ends up having in common much, if notall, the surface of the 3D tibia arthritic model 36. In one embodiment,the tibia closed-loop process may result in a 3D volumetric anatomicaljoint solid model from the 2D images 16 via applying mathematicalalgorithms. U.S. Pat. No. 5,682,886, which was filed Dec. 26, 1995 andis incorporated by reference in its entirety herein, applies a snakealgorithm forming a continuous boundary or closed-loop. After the tibiahas been outlined, a modeling process is used to create the 3D surfacemodel, for example, through a Bezier patches method. Other 3D modelingprocesses, e.g., commercially-available 3D construction software aslisted in other parts of this Detailed Description, are applicable to 3Dsurface model generation for closed-loop, volumetric solid modeling.

In one embodiment, the closed-loop process is used to form from the 2Dimages 16 a 3D volumetric solid model 36 that is essentially the same asthe arthritic model 36 discussed with respect to [blocks 125-140] ofFIG. 1D. The 3D volumetric solid model 36 is used to create the surfacemodel 40 used in the creation of the “jig data” 46 discussed withrespect to [blocks 145-150] of FIG. 1E.

The formation of a 3D volumetric solid model of the entire tibia upperend employs a process that may be much more memory and time intensivethan using an open-loop contour line to create a 3D model of thetargeted area 42 of the tibia upper end. Accordingly, although theclosed-loop methodology may be utilized for the systems and methodsdisclosed herein, for at least some embodiments, the open-loopmethodology may be preferred over the closed-loop methodology.

An example of a closed-loop methodology is disclosed in U.S. patentapplication Ser. No. 11/641,569 to Park, which is entitled “ImprovedTotal Joint Arthroplasty System” and was filed Jan. 19, 2007. Thisapplication is incorporated by reference in its entirety into thisDetailed Description.

As can be understood from FIGS. 12B and 2G, the imager 8 generates aplurality of image slices (16-1, 16-2 . . . 16-n) via repetitive imagingoperations [block 1000]. Each image slice 16 has an open-loop contourline (610-1, 610-2 . . . 610-n) extending along the targeted region 42in a manner as discussed with respect to FIG. 12A [block 1005]. In oneembodiment, each image slice is a two-millimeter 2D image slice 16. Thesystem 4 compiles the plurality of 2D image slices (16-1, 16-2 . . .16-n) and, more specifically, the plurality of open-loop contour lines(610-1, 610-2, . . . 610-n) into the 3D femur surface computer model 40depicted in FIG. 12C [block 1010]. This process regarding the generationof the surface model 40 is also discussed in the overview section withrespect to [blocks 100-105] of FIG. 1B and [blocks 130-140] of FIG. 1D.A similar process may be employed with respect to tibia closed-loopcontour lines

As can be understood from FIG. 12C, the 3D tibia surface computer model40 is a 3D computer representation of the targeted region 42 of thetibia upper end. In one embodiment, the 3D representation of thetargeted region 42 is a 3D representation of the articulated femurcontact surfaces of the tibia proximal end. As the open-loop generated3D model 40 is a surface model of the relevant femur contacting portionsof the tibia upper end, as opposed to a 3D model of the entire surfaceof the tibia upper end as would be a result of a closed-loop contourline, the open-loop generated 3D model 40 is less time and memoryintensive to generate.

In one embodiment, the open-loop generated 3D model 40 is a surfacemodel of the femur facing end face of the tibia upper end, as opposed a3D model of the entire surface of the tibia upper end. The 3D model 40can be used to identify the area of interest or targeted region 42,which, as previously stated, may be the relevant femur contactingportions of the tibia upper end. Again, the open-loop generated 3D model40 is less time and memory intensive to generate as compared to a 3Dmodel of the entire surface of the tibia proximal end, as would begenerated by a closed-loop contour line. Thus, for at least someversions of the embodiments disclosed herein, the open-loop contour linemethodology is preferred over the closed-loop contour line methodology.However, the system 4 and method disclosed herein may employ either theopen-loop or closed-loop methodology and should not be limited to one orthe other.

Regardless of whether the 3D model 40 is a surface model of the targetedregion 42 (i.e., a 3D surface model generated from an open-loop processand acting as the arthritic model 22) or the entire femur facing endface of the tibia upper end (i.e., a 3D volumetric solid model generatedfrom a closed-loop process and acting as the arthritic model 22), thedata pertaining to the contour lines 610 can be converted into the 3Dcontour computer model 40 via the surface rendering techniques disclosedin any of the aforementioned U.S. patent applications to Park. Forexample, surface rending techniques employed include point-to-pointmapping, surface normal vector mapping, local surface mapping, andglobal surface mapping techniques. Depending on the situation, one or acombination of mapping techniques can be employed.

In one embodiment, the generation of the 3D model 40 depicted in FIG.12C may be formed by using the image slices 16 to determine locationcoordinate values of each of a sequence of spaced apart surface pointsin the open-loop region of FIG. 12B. A mathematical model may then beused to estimate or compute the 3D model 40 in FIG. 12C. Examples ofother medical imaging computer programs that may be used include, butare not limited to: Analyze from AnalyzeDirect, Inc. of Overland Park,Kans.; open-source software such as Paraview of Kitware, Inc.; InsightToolkit (“ITK”) available at www.itk.org; 3D Slicer available atwww.slicer.org; and Mimics from Materialise of Ann Arbor, Mich.

Alternatively or additionally to the aforementioned systems forgenerating the 3D model 40 depicted in FIG. 12C, other systems forgenerating the 3D model 40 of FIG. 12C include the surface renderingtechniques of the Non-Uniform Rational B-spline (“NURB”) program or theBézier program. Each of these programs may be employed to generate the3D contour model 40 from the plurality of contour lines 610.

In one embodiment, the NURB surface modeling technique is applied to theplurality of image slices 16 and, more specifically, the plurality ofopen-loop contour lines 610 of FIG. 2B. The NURB software generates a 3Dmodel 40 as depicted in FIG. 12C, wherein the 3D model 40 has areas ofinterest or targeted regions 42 that contain both a mesh and its controlpoints. For example, see Ervin et al., Landscape Modeling, McGraw-Hill,2001, which is hereby incorporated by reference in its entirety intothis Detailed Description.

In one embodiment, the NURB surface modeling technique employs thefollowing surface equation:

${{G\left( {s,t} \right)} = \frac{\sum\limits_{i = 0}^{k\; 1}{\sum\limits_{j = 0}^{k\; 2}{{W\left( {i,j} \right)}{P\left( {i,j} \right)}{b_{i}(s)}{b_{j}(t)}}}}{\sum\limits_{i = 0}^{k\; 1}{\sum\limits_{j = 0}^{k\; 2}{{W\left( {i,j} \right)}{b_{i}(s)}{b_{j}(t)}}}}},$wherein P(i,j) represents a matrix of vertices with nrows=(k1+1) andncols=(k2+1), W(i,j) represents a matrix of vertex weights of one pervertex point, b_(i)(s) represents a row-direction basis or blending ofpolynomial functions of degree M1, b_(j)(t) represents acolumn-direction basis or blending polynomial functions of degree M2, srepresents a parameter array of row-direction knots, and t represents aparameter array of column-direction knots.

In one embodiment, the Bézier surface modeling technique employs theBézier equation (1972, by Pierre Bézier) to generate a 3D model 40 asdepicted in FIG. 12C, wherein the model 40 has areas of interest ortargeted regions 42. A given Bézier surface of order (n, m) is definedby a set of (n+1)(m+1) control points k_(i,j). It maps the unit squareinto a smooth-continuous surface embedded within a space of the samedimensionality as (k_(i,j)). For example, if k are all points in afour-dimensional space, then the surface will be within afour-dimensional space. This relationship holds true for aone-dimensional space, a two-dimensional space, a fifty-dimensionalspace, etc.

A two-dimensional Bézier surface can be defined as a parametric surfacewhere the position of a point p as a function of the parametriccoordinates u, v is given by:

${p\left( {u,v} \right)} = {\sum\limits_{i = 0}^{n}{\sum\limits_{j = 0}^{m}{{B_{i}^{n}(u)}{B_{j}^{m}(v)}k_{i,j}}}}$evaluated over the unit square, where

${B_{i}^{n}(u)} = {\begin{pmatrix}n \\i\end{pmatrix}{u^{i}\left( {1 - u} \right)}^{n - i}}$is a Bernstein polynomial and

$\begin{pmatrix}n \\i\end{pmatrix} = \frac{n!}{{i!}*{\left( {n - i} \right)!}}$is the binomial coefficient. See Grune et al, On Numerical Algorithm andInteractive Visualization for Optimal Control Problems, Journal ofComputation and Visualization in Science, Vol. 1, No. 4, July 1999,which is hereby incorporated by reference in its entirety into thisDetailed Description.

Various other surface rendering techniques are disclosed in otherreferences. For example, see the surface rendering techniques disclosedin the following publications: Lorensen et al., Marching Cubes: A highResolution 3d Surface Construction Algorithm, Computer Graphics, 21-3:163-169, 1987; Farin et al., NURB Curves & Surfaces: From ProjectiveGeometry to Practical Use, Wellesley, 1995; Kumar et al, RobustIncremental Polygon Triangulation for Surface Rendering, WSCG, 2000;Fleischer et al., Accurate Polygon Scan Conversion Using Half-OpenIntervals, Graphics Gems III, p. 362-365, code: p. 599-605, 1992; Foleyet al., Computer Graphics: Principles and Practice, Addison Wesley,1990; Glassner, Principles of Digital Image Synthesis, Morgan Kaufmann,1995, all of which are hereby incorporated by reference in theirentireties into this Detailed Description.

g. Selecting a Jig Blank Most Similar in Size and/or Configuration tothe Size of the Patient's Tibia Upper End.

As mentioned above, an arthroplasty jig 2, such as a tibia jig 2Bincludes an interior portion 104 and an exterior portion 106. The tibiajig 2B is formed from a tibia jig blank 50B, which, in one embodiment,is selected from a finite number of femur jig blank sizes. The selectionof the tibia jig blank 50B is based on a comparison of the dimensions ofthe patient's tibia upper end 604 to the dimensions and/orconfigurations of the various sizes of tibia jig blanks 50B to selectthe tibia jig blank 50B most closely resembling the patient's tibiaupper end 604 with respect to size and/or configuration. This selectedtibia jig blank 50B has an outer or exterior side or surface 632 thatforms the exterior portion 632 of the tibia jig 2B. The 3D surfacecomputer model 40 discussed with respect to the immediately precedingsection of this Detail Description is used to define a 3D surface 40into the interior side 630 of the computer model of a tibia jig blank50B. Furthermore, in some embodiments, the overestimation of theprocedure described below may be used to adjust the 3D surface model 40.

By selecting a tibia jig blank 50B with an exterior portion 632 close insize to the patient's upper tibia end 604, the potential for an accuratefit between the interior portion 630 and the patient's tibia isincreased. Also, the amount of material that needs to be machined orotherwise removed from the jig blank 50B is reduced, thereby reducingmaterial waste and manufacturing time.

For a discussion of a method of selecting a jig blank 50 most closelycorresponding to the size and/or configuration of the patient's uppertibia end, reference is first made to FIGS. 13A-14B. FIG. 13A is a topperspective view of a right tibia cutting jig blank 50BR havingpredetermined dimensions. FIG. 13B is a bottom perspective view of thejig blank 50BR depicted in FIG. 13A. FIG. 13C is plan view of anexterior side or portion 232 of the jig blank 50BR depicted in FIG. 13A.FIG. 14A is a plurality of available sizes of right tibia jig blanks50BR, each depicted in the same view as shown in FIG. 13C. FIG. 14B is aplurality of available sizes of left tibia jig blanks, each depicted inthe same view as shown in FIG. 13C.

A common jig blank 50, such as the right jig blank 50BR depicted inFIGS. 13A-13C and intended for creation of a right tibia jig that can beused with a patient's right tibia, may include a medial tibia footprojection 648 for mating with the medial tibia plateau, a lateral tibiafoot projection 650 for mating with the lateral tibia plateau, aposterior edge 640, an anterior edge 642, a lateral edge 644, a medialedge 646, the exterior side 632 and the interior side 630. The jig blank50BR of FIGS. 13A-13C may be any one of a number of right tibia jigblanks 50BR available in a limited number of standard sizes. Forexample, the jig blank 50BR of FIGS. 13A-13C may be an i-th right tibiajig blank, where i=1, 2, 3, 4, . . . m and m represents the maximumnumber of right tibia jig blank sizes. As indicated in FIG. 13C, theanterior-posterior extent TAi of the jig blank 50BR is measured from theanterior edge 642 to the posterior edge 640 of the jig blank 50BR. Themedial-lateral extent TMi of the jig blank 50BR is measured from thelateral edge 644 to the medial edge 646 of the jig blank 50BR.

As can be understood from FIG. 14A, a limited number of right tibia jigblank sizes may be available for selection as the right tibia jig blanksize to be machined into the right tibia cutting jig 2B. For example, inone embodiment, there are three sizes (m=3) of right tibia jig blanks50BR available. As can be understood from FIG. 13C, each tibia jig blank50BR has an anterior-posterior/medial-lateral aspect ratio defined asTAi to TMi (e.g., “TAi/TMi” aspect ratio). Thus, as can be understoodfrom FIG. 14A, jig blank 50BR-1 has an aspect ratio defined as“TA₁/TM₁”, jig blank 50BR-2 has an aspect ratio defined as “TA₂/TM₂”,and jig blank 50BR-3 has an aspect ratio defined as “TA₃/TM₃”.

The jig blank aspect ratio is utilized to design right tibia jigs 2Bdimensioned specific to the patient's right tibia features. In oneembodiment, the jig blank aspect ratio can be the exterior dimensions ofthe right tibia jig 2B. In another embodiment, the jig blank aspectratio can apply to the right tibia jig fabrication procedure forselecting the right jig blank 50BR having parameters close to thedimensions of the desired right tibia jig 2B. This embodiment canimprove the cost efficiency of the right tibia jig fabrication processbecause it reduces the amount of machining required to create thedesired jig 2 from the selected jig blank 50.

In FIG. 14A there is a single jig blank aspect ratio depicted for thecandidate tibia jig blank sizes. In embodiments having a greater numberof jig blank aspect ratios for the candidate tibia jig blank sizes, FIG.14A would be similar to FIG. 4A and would have an N-1 direction, andpotentially N-2 and N-3 directions, representing increasing jig blankaspect ratios. The relationships between the various tibia jig blankaspect ratios would be similar to those discussed with respect to FIG.4A for the femur jig blank aspect ratios.

As can be understood from the plot 900 depicted in FIG. 17 and discussedlater in this Detailed Discussion, the E-1 direction corresponds to thesloped line joining Group 1, Group 2 and Group 3 in the plot 900.

As indicated in FIG. 14A, along direction E-1, the jig blank aspectratios remain the same among jigs blanks 50BR-1, 50BR-2 and 50BR-3,where “TA₁/TM₁”=“TA₂/TM₂”=“TA₃/TM₃”. However, comparing to jig blank50BR-1, jig blank 50BR-2 is dimensioned larger and longer than jig blank50BR-1. This is because the TA₂ value for jig blank 50BR-2 increasesproportionally with the increment of its TM₂ value in certain degrees inall X, Y, and Z-axis directions. In a similar fashion, jig blank 50BR-3is dimensioned larger and longer than jig blank 50BR-2 because the TA₃increases proportionally with the increment of its TM₃ value in certaindegrees in all X, Y, and Z-axis directions. One example of the incrementcan be an increase from 5% to 20%. In embodiments where there areadditional aspect ratios available for the tibia jig blank sizes, as wasillustrated in FIG. 4A with respect to the femur jig blank sizes, therelationship between tibia jig blank sizes may be similar to thatdiscussed with respect to FIGS. 4A and 14A.

As can be understood from FIG. 14B, a limited number of left tibia jigblank sizes may be available for selection as the left tibia jig blanksize to be machined into the left tibia cutting jig 2B. For example, inone embodiment, there are three sizes (m=3) of left tibia jig blanks50BL available. As can be understood from FIG. 13C, each tibia jig blank50BL has an anterior-posterior/medial-lateral aspect ratio defined asTAi to TMi (e.g., “TAi/TMi” aspect ratio). Thus, as can be understoodfrom FIG. 14B, jig blank 50BL-1 has an aspect ratio defined as“TA₁/TM₁”, jig blank 50BL-2 has an aspect ratio defined as “TA₂/TM₂”,and jig blank 50BL-3 has an aspect ratio defined as “TA₃/TM₃”.

The jig blank aspect ratio is utilized to design left tibia jigs 2Bdimensioned specific to the patient's left tibia features. In oneembodiment, the jig blank aspect ratio can be the exterior dimensions ofthe left tibia jig 2B. In another embodiment, the jig blank aspect ratiocan apply to the left tibia jig fabrication procedure for selecting theleft jig blank 50BL having parameters close to the dimensions of thedesired left tibia jig 2B. This embodiment can improve the costefficiency of the left tibia jig fabrication process because it reducesthe amount of machining required to create the desired jig 2 from theselected jig blank 50.

In FIG. 14B there is a single jig blank aspect ratio depicted for thecandidate tibia jig blank sizes. In embodiments having a greater numberof jig blank aspect ratios for the candidate tibia jig blank sizes, FIG.14B would be similar to FIG. 4B and would have an N-1 direction, andpotentially N-2 and N-3 directions, representing increasing jig blankaspect ratios. The relationships between the various tibia jig blankaspect ratios would be similar to those discussed with respect to FIG.4B for the femur jig blank aspect ratios.

As indicated in FIG. 14B, along direction E-1, the jig blank aspectratios remain the same among jigs blanks 50BL-1, 50BL-2 and 50BL-3,where “TA₁/TM₁”=“TA₂/TM₂”=“TA₃/TM₃”. However, comparing to jig blank50BL-1, jig blank 50BL-2 is dimensioned larger and longer than jig blank50BL-1. This is because the TA₂ value for jig blank 50BL-2 increasesproportionally with the increment of its TM₂ value in certain degrees inall X, Y, and Z-axis directions. In a similar fashion, jig blank 50BL-3is dimensioned larger and longer than jig blank 50BL-2 because the TA₃increases proportionally with the increment of its TM₃ value in certaindegrees in all X, Y, and Z-axis directions. One example of the incrementcan be an increase from 5% to 20%. In embodiments where there areadditional aspect ratios available for the tibia jig blank sizes, as wasillustrated in FIG. 4B with respect to the femur jig blank sizes, therelationship between tibia jig blank sizes may be similar to thatdiscussed with respect to FIGS. 4B and 14B.

The dimensions of the upper or knee joint forming end 604 of thepatient's tibia 20 can be determined by analyzing the 3D surface model40 or 3D arthritic model 36 in a manner similar to those discussed withrespect to the jig blanks 50. For example, as depicted in FIG. 15, whichis an axial view of the 3D surface model 40 or arthritic model 36 of thepatient's right tibia 20 as viewed in a direction extending proximal todistal, the upper end 604 of the surface model 40 or arthritic model 36may include an anterior edge 660, a posterior edge 662, a medial edge664 and a lateral edge 666. The tibia dimensions may be determined forthe top end face or femur articulating surface 604 of the patient'stibia 20 via analyzing the 3D surface model 40 of the 3D arthritic model36. These tibia dimensions can then be utilized to configure tibia jigdimensions and select an appropriate tibia jig.

As shown in FIG. 15, the anterior-posterior extent tAP of the upper end604 of the patient's tibia 20 (i.e., the upper end 604 of the surfacemodel 40 of the arthritic model 36, whether formed via open orclosed-loop analysis) is the length measured from the anterior edge 660of the tibia plateau to the posterior edge 662 of the tibia plateau. Themedial-lateral extent tML of the upper end 604 of the patient's tibia 20is the length measured from the medial edge 664 of the medial tibiaplateau to the lateral edge 666 of the lateral tibia plateau.

In one embodiment, the anterior-posterior extent tAP and medial-lateralextent tML of the tibia upper end 604 can be used for an aspect ratiotAP/tML of the tibia upper end. The aspect ratios tAP/tML of a largenumber (e.g., hundreds, thousands, tens of thousands, etc.) of patientknees can be compiled and statistically analyzed to determine the mostcommon aspect ratios for jig blanks that would accommodate the greatestnumber of patient knees. This information may then be used to determinewhich one, two, three, etc. aspect ratios would be most likely toaccommodate the greatest number of patient knees.

The system 4 analyzes the upper ends 604 of the patient's tibia 20 asprovided via the surface model 40 of the arthritic model 36 (whether thearthritic model 36 is an 3D surface model generated via an open-loop ora 3D volumetric solid model generated via a closed-loop process), toobtain data regarding anterior-posterior extent tAP and medial-lateralextent tML of the tibia upper ends 604. As can be understood from FIG.16, which depicts the selected model jig blank 50BR of FIG. 13Csuperimposed on the model tibia upper end 604 of FIG. 15, the tibiadimensional extents tAP, tML are compared to the jig blank dimensionalextents TAi, TMi to determine which jig blank model to select as thestarting point for the machining process and the exterior surface modelfor the jig model.

As shown in FIG. 16, a prospective right tibia jig blank 50BR issuperimposed to mate with the right tibia upper end 604 of the patient'sanatomical model as represented by the surface model 40 or arthriticmodel 36. In one embodiment, the jig blank 50BR may cover the anteriorapproximately two thirds of the tibia plateau, leaving the posteriorapproximately one third of the tibia exposed. Included in the exposedportion of the tibia plateau are lateral and medial exposed regions ofthe tibia plateau, as respectively represented by regions q1 and q2 inFIG. 16. Specifically, exposed region q1 is the region of the exposedtibia plateau between the tibia and jig blank lateral edges 666, 644,and exposed region q2 is the region of the exposed tibia plateau betweenthe tibia and jig blank medial edges 664, 646.

By obtaining and employing the tibia anterior-posterior tAP data and thetibia medial-lateral tML data, the system 4 can size the tibia jig blank50BR according to the following formula: jTML=tML−q1−q2, wherein jTML isthe medial-lateral extent of the tibia jig blank 50BR. In oneembodiment, q1 and q2 will have the following ranges: 2 mm≦q1≦4 mm; and2 mm≦q2≦4 mm. In another embodiment, q1 will be approximately 3 mm andq2 will approximately 3 mm.

FIG. 17A is an example scatter plot 900 for selecting from a pluralityof candidate jig blanks sizes a jig blank size appropriate for the upperend 604 of the patient's tibia 20. In one embodiment, the X-axisrepresents the patient's tibia medial-lateral length tML in millimeters,and the Y-axis represents the patient's tibia anterior-posterior lengthtAP in millimeters. In one embodiment, the plot 900 is divided into anumber of jig blank size groups, where each group encompasses a regionof the plot 900 and is associated with a specific parameter TM_(r) of aspecific candidate jig blank size.

In one embodiment, the example scatter plot 900 depicted in FIG. 17A hasthree jig blank size groups, each group pertaining to a single candidatejig blank size. However, depending on the embodiment, a scatter plot 900may have a greater or lesser number of jig blank size groups. The higherthe number of jig blank size groups, the higher the number of thecandidate jig blank sizes and the more dimension specific a selectedcandidate jig blank size will be to the patient's knee features and theresulting jig 2. The more dimension specific the selected candidate jigblank size, the lower the amount of machining required to produce thedesired jig 2 from the selected jig blank 50.

Conversely, the lower the number of jig blank size groups, the lower thenumber of candidate jig blank sizes and the less dimension specific aselected candidate jig blank size will be to the patient's knee featuresand the resulting jig 2. The less dimension specific the selectedcandidate jig blank size, the higher the amount of machining required toproduce the desired jig 2 from the selected jig blank 50, adding extraroughing during the jig fabrication procedure.

The tibia anterior-posterior length tAP may be relevant because it mayserve as a value for determining the aspect ratio TA_(i)/TM_(j). fortibia jig blanks 50B such as those discussed with respect to FIGS.13C-14B and 17A. Despite this, in some embodiments, tibiaanterior-posterior length TA_(i) of the candidate jig blanks may not bereflected in the plot 900 depicted in FIG. 17A or the relationshipdepicted in FIG. 16 because in a practical setting for some embodiments,tibia jig anterior-posterior length may be less significant than tibiajig medial-lateral length. For example, although a patient's tibiaanterior-posterior distance varies according to their knee features, thelength of the foot projection 800, 802 (see FIG. 20A) of a tibia jig 2Bis simply increased without the need to create a jig blank or jig thatis customized to correspond to the tibia anterior-posterior length TAi.In other words, in some embodiments, the only difference inanterior-posterior length between various tibia jigs is the differencein the anterior-posterior length of their respective foot projections800, 802.

In some embodiments, as can be understood from FIGS. 16 and 21, theanterior-posterior length of a tibia jig 2B, with its foot projection800, 802, covers approximately half of the tibia plateau. Due in part tothis “half” distance coverage, which varies from patient-to-patient byonly millimeters to a few centimeter, in one embodiment, theanterior-posterior length of the jig may not be of a significantconcern. However, because the jig may cover a substantial portion of themedial-lateral length of the tibia plateau, the medial-lateral length ofthe jig may be of substantial significance as compared to theanterior-posterior length.

While in some embodiments the anterior-posterior length of a tibia jig2B may not be of substantial significance as compared to themedial-lateral length, in some embodiments the anterior-posterior lengthof the tibia jig is of significance. In such an embodiment, jig sizesmay be indicated in FIG. 17A by their aspect ratios TA_(i)/TM_(i) asopposed to just TM_(i). In other words, the jig sizes may be depicted inFIG. 17A in a manner similar to that depicted in FIG. 7A. Furthermore,in such embodiments, FIGS. 14A and 14B may have additional jig blankratios similar to that depicted in FIGS. 4A and 4B. As a result, theplot 900 of 17A may have additional diagonal lines joining the jig blanksizes belonging to each jig blank ratio in a manner similar to thatdepicted in plot 300 of FIG. 7A. Also, in FIG. 17A and in a mannersimilar to that shown in FIG. 7A, there may be additional horizontallines dividing plot 900 according to anterior-posterior length torepresent the boundaries of the various jig blank sizes.

As can be understood from FIG. 17A, in one embodiment, the three jigblank size groups of the plot 900 have parameters TM_(r), TA_(r) asfollows. Group 1 has parameters TM₁, TA1. TM₁ represents themedial-lateral extent of the first tibia jig blank size, wherein TM₁=70mm. TA₁ represents the anterior-posterior extent of the first femoraljig blank size, wherein TA₁=62 mm. Group 1 covers the patient's tibiatML and tAP data wherein 55 mm<tML<70 mm and 45 mm<tAP<75 mm.

Group 2 has parameters TM₂, TA2. TM₂ represents the medial-lateralextent of the second tibia jig blank size, wherein TM₂=85 mm. TA₂represents the anterior-posterior extent of the second femoral jig blanksize, wherein TA₂=65 mm. Group 2 covers the patient's tibia tML and tAPdata wherein 70 mm<tML<85 mm and 45 mm<tAP<75 mm.

Group 3 has parameters TM₃, TA3. TM₃ represents the medial-lateralextent of the third tibia jig blank size, wherein TM₃=100 mm. TA₃represents the anterior-posterior extent of the second femoral jig blanksize, wherein TA₃=68.5 mm. Group 3 covers the patient's tibia tML andtAP data wherein 85 mm<tML<100 mm and 45 mm<tAP<75 mm.

In some embodiments and in contrast to the selection process for thefemur jig blanks discussed with respect to FIGS. 3A-7B, the tibia jigblank selection process discussed with respect to FIGS. 13A-17B may onlyconsider or employ the medial-lateral tibia jig value jTML and relatedmedial-lateral values TMi, tML. Accordingly, in such embodiments, theanterior-posterior tibia jig value JTAP and related anterior-posteriorvalues TAi, tAP for the tibia jig and tibia plateau are not considered.

As can be understood from FIG. 17B, which is a flow diagram illustratingan embodiment of a process of selecting an appropriately sized jigblank, the bone medial-lateral extent tML is determined for the upperend 604 of the surface model 40 of the arthritic model 36 [block 3000].The medial-lateral bone extent tML of the upper end 604 ismathematically modified according to the above discussed jTML formula toarrive at the minimum tibia jig blank medial-lateral extent jTML [block3010]. The mathematically modified bone medial-lateral extent tML or,more specifically, the minimum tibia jig blank medial-lateral extentjTML is referenced against the jig blank dimensions in the plot 900 ofFIG. 17A [block 3020]. The plot 900 may graphically represent theextents of candidate tibia jig blanks forming a jig blank library. Thetibia jig blank 50B is selected to be the jig blank size having thesmallest extents that are still sufficiently large to accommodate theminimum tibia jig blank medial-lateral extent jTML [block 3030].

In one embodiment, the exterior of the selected jig blank size is usedfor the exterior surface model of the jig model, as discussed below. Inone embodiment, the selected jig blank size corresponds to an actual jigblank that is placed in the CNC machine and milled down to the minimumtibia jig blank anterior-posterior and medial-lateral extents jTAP, jTMLto machine or otherwise form the exterior surface of the tibia jig 2B

The method outlined in FIG. 17B and in reference to the plot 900 of FIG.17A can be further understood from the following example. As measured inFIG. 16 with respect to the upper end 604 of the patient's tibia 20, theextents of the patient's tibia are as follows: tML=85.2 mm [block 3000].As previously mentioned, the upper end 604 may be part of the surfacemodel 40 of the arthritic model 36. Once the tML measurement isdetermined from the upper end 604, the corresponding jig jTML data canbe determined via the above-described jTML formula: jTML=tML−q1−q2,wherein q1=3 mm and q2=3 mm [block 3010]. The result of the jTML formulais jTML=79.2 mm.

As can be understood from the plot 900 of FIG. 17A, the determined jigdata (i.e., jTML=79.2 mm) falls in Group 2 of the plot 900. Group 2 hasthe predetermined tibia jig blank parameters (TM₂) of TM₂=85 mm. Thispredetermined tibia jig blank parameter is the smallest of the variousgroups that are still sufficiently large to meet the minimum tibia blankextents jTML [block 3020]. This predetermined tibia jig blank parameters(TM₂=85 mm) may be selected as the appropriate tibia jig blank size[block 3030].

In one embodiment, the predetermined tibia jig blank parameter (85 mm)can apply to the tibia exterior jig dimensions as shown in FIG. 13C. Inother words, the jig blank exterior is used for the jig model exterioras discussed with respect to FIGS. 18A-19C. Thus, the exterior of thetibia jig blank 50B undergoes no machining, and the unmodified exteriorof the jig blank 50B with its predetermined jig blank parameter (85 mm)serves as the exterior of the finished tibia jig 2B.

In another embodiment, the tibia jig blank parameter (85 mm) can beselected for jig fabrication in the machining process. Thus, a tibia jigblank 50B having a predetermined parameter (85 mm) is provided to themachining process such that the exterior of the tibia jig blank 50B willbe machined from its predetermined parameter (85 mm) down to the desiredtibia jig parameter (79.2 mm) to create the finished exterior of thetibia jig 2B. As the predetermined parameter (85 mm) is selected to berelatively close to the desired femur jig parameter (79.2 mm), machiningtime and material waste are reduced.

While it may be advantageous to employ the above-described jig blankselection method to minimize material waste and machining time, in someembodiments, a jig blank will simply be provided that is sufficientlylarge to be applicable to all patient bone extents tML. Such a jig blankis then machined down to the desired jig blank extent jTML, which serveas the exterior surface of the finished jig 2B.

In one embodiment, the number of candidate jig blank size groupsrepresented in the plot 900 is a function of the number of jig blanksizes offered by a jig blank manufacturer. For example, a first plot 900may pertain only to jig blanks manufactured by company A, which offersthree jig blank sizes. Accordingly, the plot 900 has three jig blanksize groups. A second plot 900 may pertain only to jig blanksmanufactured by company B, which offers six jig blank size groups.Accordingly, the second plot 900 has six jig blank size groups.

A plurality of candidate jig blank sizes exist, for example, in a jigblank library as represented by the plot 900 of FIG. 17B. While eachcandidate jig blank may have a unique combination of anterior-posteriorand medial-lateral dimension sizes, in some embodiments, two or more ofthe candidate jig blanks may share a common aspect ratio tAP/tML orconfiguration. The candidate jig blanks of the library may be groupedalong sloped lines of the plot 900 according to their aspect ratiostAP/tML.

In one embodiment, the jig blank aspect ratio tAP/tML may be used totake a workable jig blank configuration and size it up or down to fitlarger or smaller individuals.

As can be understood from FIG. 17A, a series of 98 OA patients havingknee disorders were entered into the plot 900 as part of a tibia jigdesign study. Each patient's tibia tAP and tML data was measured. Eachpatient tibia tML data was modified via the above-described jTML formulato arrive at the patient's jig blank data (jFML). The patient's jigblank data was then entered into the plot 900 as a point. As can beunderstood from FIG. 17A, no patient point lies outside the parametersof an available group. Such a process can be used to establish groupparameters and the number of needed groups.

In one embodiment, the selected jig blank parameters can be the tibiajig exterior dimensions that are specific to patient's knee features. Inanother embodiment, the selected jig blank parameters can be chosenduring fabrication process.

h. Formation of 3D Tibia Jig Model.

For a discussion of an embodiment of a method of generating a 3D tibiajig model 746 generally corresponding to the “integrated jig data” 48discussed with respect to [block 150] of FIG. 1E, reference is made toFIGS. 13A-13C, FIGS. 18A-18B, FIGS. 19A-19D and FIG. 20A-20B. FIGS.13A-13C are various views of a tibia jig blank 50B. FIGS. 18A-18B are,respectively, exterior and interior perspective views of a tibia jigblank exterior surface model 632M. FIGS. 19A-19D are exteriorperspective views of the tibia jig blank exterior model 632M and bonesurface model 40 being combined. FIGS. 20A and 20B are, respectively,exterior and interior perspective views of the resulting tibia jig model746 after having “saw cut and drill hole data” 44 integrated into thejig model 746 to become an integrated or complete jig model 748generally corresponding to the “integrated jig data” 48 discussed withrespect to [block 150] of FIG. 1E.

As can be understood from FIGS. 13A-13C, the jig blank 50B, which hasselected predetermined dimensions as discussed with respect to FIGS. 17Aand 17B, includes an interior surface 630 and an exterior surface 632.The exterior surface model 632M depicted in FIGS. 18A and 18B isextracted or otherwise created from the exterior surface 632 of the jigblank model 50B. Thus, the exterior surface model 632M is based on thejig blank aspect ratio of the tibia jig blank 50B selected as discussedwith respect to FIGS. 17A and 17B and is dimensioned specific to thepatient's knee features. The tibia jig surface model 632M can beextracted or otherwise generated from the jig blank model 50B of FIGS.13A-13C by employing any of the computer surface rendering techniquesdescribed above.

As can be understood from FIGS. 19A-19C, the exterior surface model 632Mis combined with the tibia surface model 40 to respectively form theexterior and interior surfaces of the tibia jig model 746. The tibiasurface model 40 represents the interior or mating surface of the tibiajig 2B and corresponds to the tibia arthroplasty target area 42. Thus,the model 40 allows the resulting tibia jig 2B to be indexed to thearthroplasty target area 42 of the patient's tibia 20 such that theresulting tibia jig 2B will matingly receive the arthroplasty targetarea 42 during the arthroplasty procedure. The two surface models 632M,40 combine to provide a patient-specific jig model 746 for manufacturingthe tibia jig 2B.

As can be understood from FIGS. 19B and 19C, once the models 632M, 40are properly aligned, a gap will exist between the two models 632M, 40.An image sewing method or image sewing tool is applied to the alignedmodels 632M, 40 to join the two surface models together to form the 3Dcomputer generated jig model 746 of FIG. 19B into a single-piece,joined-together, and filled-in jig model 746 similar in appearance tothe integrated jig model 748 depicted in FIGS. 20A and 20B. In oneembodiment, the jig model 746 may generally correspond to thedescription of the “jig data” 46 discussed with respect [block 145] ofFIG. 1E.

As can be understood from FIGS. 19B-19D, 20A and 20B, the geometric gapsbetween the two models 632M, 40, some of which are discussed below withrespect to thicknesses V₁, V₂ and V₃, may provide certain space betweenthe two surface models 632M, 40 for slot width and length and drill bitlength for receiving and guiding cutting tools during TKA surgery.Because the resulting tibia jig model 748 depicted in FIGS. 20A and 20Bmay be a 3D volumetric model generated from 3D surface models 632M, 40,a space or gap should be established between the 3D surface models 632M,40. This allows the resulting 3D volumetric jig model 748 to be used togenerate an actual physical 3D volumetric tibia jig 2B.

In some embodiments, the image processing procedure may include a modelrepair procedure for repairing the jig model 746 after alignment of thetwo models 632M, 40. For example, various methods of the model repairinginclude, but are not limit to, user-guided repair, crack identificationand filling, and creating manifold connectivity, as described in:Nooruddin et al., Simplification and Repair of Polygonal Models UsingVolumetric Techniques (IEEE Transactions on Visualization and ComputerGraphics, Vol. 9, No. 2, April-June 2003); C. Erikson, Error Correctionof a Large Architectural Model: The Henderson County Courthouse(Technical Report TR95-013, Dept. of Computer Science, Univ. of NorthCarolina at Chapel Hill, 1995); D. Khorramabdi, A Walk through thePlanned CS Building (Technical Report UCB/CSD 91/652, Computer ScienceDept., Univ. of California at Berkeley, 1991); Morvan et al., IVECS: AnInteractive Virtual Environment for the Correction of .STL files (Proc.Conf. Virtual Design, August 1996); Bohn et al., A Topology-BasedApproach for Shell-Closure, Geometric Modeling for Product Realization,(P. R. Wilson et al., pp. 297-319, North-Holland, 1993); Barequet etal., Filling Gaps in the Boundary of a Polyhedron, Computer AidedGeometric Design (vol. 12, no. 2, pp. 207-229, 1995); Barequet et al.,Repairing CAD Models (Proc. IEEE Visualization '97, pp. 363-370, October1997); and Gueziec et al., Converting Sets of Polygons to ManifoldSurfaces by Cutting and Stitching, (Proc. IEEE Visualization 1998, pp.383-390, October 1998). Each of these references is incorporated intothis Detailed Description in their entireties.

As can be understood from FIGS. 20A and 20B, the integrated jig model748 may include several features based on the surgeon's needs. Forexample, the jig model 748 may include a slot feature 30 for receivingand guiding a bone saw and drill holes 32 for receiving and guiding bonedrill bits. As can be understood from FIGS. 19B and 19C, to providesufficient structural integrity to allow the resulting tibia jig 2B tonot buckle or deform during the arthroplasty procedure and to adequatelysupport and guide the bone saw and drill bits, the gap between themodels 232M, 40 may have the following offsets V₁, V₂, and V₃.

As can be understood from FIGS. 19B-20B, in one embodiment, thickness V₁extends along the length of the posterior drill holes 32P between themodels 632M, 40 and is for supporting and guiding a bone drill receivedtherein during the arthroplasty procedure. Thickness V₁ may be at leastapproximately four millimeters or at least approximately fivemillimeters thick. The diameter of the posterior drill holes 32P may beconfigured to receive a cutting tool of at least one-third inches.

Thickness V₂ extends is the thickness of the jig foots 800, 802 betweenthe inner and exterior surfaces 40, 632M. The thickness providesadequate structural strength for jig foots 800, 802, to resist bucklingand deforming of the jig to manufacture and use. Thickness V₂ may be atleast approximately five millimeters or at least eight millimetersthick.

Thickness V₃ extends along the length of a saw slot 30 between themodels 632M, 40 and is for supporting and guiding a bone saw receivedtherein during the arthroplasty procedure. Thickness V₃ may be at leastapproximately 10 mm or at least 15 mm thick.

In addition to providing sufficiently long surfaces for guiding drillbits or saws received therein, the various thicknesses V₁, V₂, V₃ arestructurally designed to enable the tibia jig 2B to bear vigorous tibiacutting, drilling and reaming procedures during the TKR surgery.

As indicated in FIGS. 20A and 20B, the exterior portion or side 106 ofthe integrated jig model 748 may include: feature or jig foot 800 thatextends over and matches the patient's medial portion of the tibiaplateau; feature or jig foot 802 that extends over and matches thepatient's lateral portion of the tibia plateau; projection 804 thatextends downward from the upper exterior surface 632 of the tibia jig2B; and a flat portion of the exterior surface 632 that provides ablanked labeling area for listing information regarding the patient,surgeon or/and the surgical procedure. Also, as discussed above, theintegrated jig model 748 may include the saw cut slot 30 and the drillholes 32. The inner portion or side 104 of the jig model 748 (and theresulting tibia jig 2B) is the tibia surface model 40, which willmatingly receive the arthroplasty target area 42 of the patient's tibia20 during the arthroplasty procedure.

As can be understood by referring to [block 105] of FIG. 1B and FIGS.12A-12C, in one embodiment when cumulating the image scans 16 togenerate the one or the other of the models 40, 22, the models 40, 22are referenced to point P, which may be a single point or a series ofpoints, etc. to reference and orient the models 40, 22 relative to themodels 22, 28 discussed with respect to FIG. 1C and utilized for POP.Any changes reflected in the models 22, 28 with respect to point P(e.g., point P becoming point P′) on account of the POP is reflected inthe point P associated with the models 40, 22 (see [block 135] of FIG.1D). Thus, as can be understood from [block 140] of FIG. 1D and FIGS.19A-19C, when the jig blank exterior surface model 632M is combined withthe surface model 40 (or a surface model developed from the arthriticmodel 22) to create the jig model 746, the jig model 746 is referencedand oriented relative to point P′ and is generally equivalent to the“jig data” 46 discussed with respect to [block 145] of FIG. 1E.

Because the jig model 746 is properly referenced and oriented relativeto point P′, the “saw cut and drill hole data” 44 discussed with respectto [block 125] of FIG. 1E can be properly integrated into the jig model746 to arrive at the integrated jig model 748 depicted in FIGS. 20A-20B.The integrated jig model 748 includes the saw cuts 30, drill holes 32and the surface model 40. Thus, the integrated jig model 748 isgenerally equivalent to the “integrated jig data” 48 discussed withrespect to [block 150] of FIG. 1E.

As can be understood from FIG. 21, which illustrates a perspective viewof the integrated jig model 748 mating with the “arthritic model” 22,the interior surface 40 of the jig model 748 matingly receives thearthroplasty target area 42 of the tibia upper end 604 such that the jigmodel 748 is indexed to mate with the area 42. Because of thereferencing and orientation of the various models relative to the pointsP, P′ throughout the procedure, the saw cut slot 30 and drill holes 32are properly oriented to result in saw cuts and drill holes that allow aresulting tibia jig 2B to restore a patient's joint to a pre-degeneratedcondition.

As indicated in FIG. 21, the integrated jig model 748 may include a jigbody 850, a medial tibia plateau covering projection 852, a lateraltibia plateau covering projection 854, a lower portion 856 extendingform the body 850, posterior drill holes 32P, anterior drill holes 32A,a saw slot 30 and an upper flat portion 857 for receiving thereonpatient, surgery and physician data. The projections 852, 854 extendover their respective medial and lateral tibia plateau portions. Theprojections 852, 854, 856, 857 extend integrally from the jig body 850.

As can be understood from [blocks 155-165] of FIG. 1E, the integratedjig 748 or, more specifically, the integrated jig data 48 can be sent tothe CNC machine 10 to machine the tibia jig 2B from the selected jigblank 50B. For example, the integrated jig data 48 may be used toproduce a production file that provides automated jig fabricationinstructions to a rapid production machine 10, as described in thevarious Park patent applications referenced above. The rapid productionmachine 10 then fabricates the patient-specific arthroplasty tibia jig2B from the tibia jig blank 50B according to the instructions.

The resulting tibia jig 2B may have the features of the integrated jigmodel 748. Thus, as can be understood from FIG. 21, the resulting tibiajig 2B may have the slot 30 and the drilling holes 32 formed on theprojections 852, 854, 856, 857, depending on the needs of the surgeon.The drilling holes 32 are configured to prevent the possible IR/ER(internal/external) rotational axis misalignment between the tibiacutting jig 2B and the patient's damaged joint surface during theproximal tibia cut portion of the TKR procedure. The slot 30 isconfigured to accept a cutting instrument, such as a reciprocating slawblade for transversely cutting during the proximal tibia cut portion ofthe TKR.

i. Overestimation Process

As mentioned above in Subsection a of this Detailed Description, certainregions of the 3D surface models 40 may be a more accuraterepresentation of the actual patient bone surface than other regionsand/or may be more readily machined. For example, because of limitationsin the medical imaging process (e.g., having to rely on a finite numberof image slices 16 as opposed to an infinite number of image slices,volume averaging issues, and issues presented by irregular contours dueto the presence of osteophytes, fat tissue, broken cartilage, etc.), the3D surface models 40 in certain regions may not be an accuraterepresentation of the corresponding actual bone surfaces of thearthroplasty target areas. As a result, a bone mating surface of anactual jig 2 based upon such less accurate data may end up having aninterfering fit as opposed to a mating fit with the arthroplasty targetarea of the actual bone surfaces.

With respect to machining, the size of the tooling used to machine thebone mating surface of the actual jig may exceed the size of certainfeatures in the 3D surface models 40. As a result, the CNC machine maynot be able to accurately machine the bone mating surface of the actualjig to match the 3D surface models.

To address these issues presented by the imaging and machininglimitations, the 3D surface models 40, or more specifically, the contourlines 210, 210′ used to generate the 3D surface models, may be subjectedto the overestimation process described below. The result of theoverestimation process is an actual jig with: (1) bone mating surfacesthat matingly receive and contact certain regions of the actual bonesurface of the arthroplasty target region, wherein the certain regionscorrespond to regions of the actual bone surface that can be accuratelyand reliably 3D computer modeled and actually machined; and (2)bone-facing surfaces of the jig (i.e., those surfaces of the jig thatface the bone when the bone mating surfaces of the jig matingly receiveand contact the bone surfaces of the arthroplasty target region) thatavoid contact with certain other regions of the actual bone surface ofthe arthroplasty target region, wherein the certain other regionscorrespond to regions of the actual bone surface that are less likely tobe accurately and reliably 3D computer modeled and/or less likely to beactually machined.

In creating bone-facing surfaces of the jig that correspond to bonesurface regions that are less likely to be accurately 3D modeled and/oractually machined, the overestimation process overestimates or moves thecontour lines 210 away or outward from the bone area of the image slice16 such that the CNC machine will be caused to over-machine along theoverestimated contour line. This outward displacement of the contourline 210 results in the jig's bone-facing surface corresponding to theoverestimated contour line being spaced apart from the correspondingactual bone surface of the arthroplasty target region when the jig'sbone mating surface matingly receives and contacts the arthroplastytarget region.

Due to the overestimation process, in one embodiment, the contactbetween the jig's bone mating surface and the bone surface of thearthroplasty target region is limited to those regions of thearthroplasty target region that can be accurately and reliably 3Dcomputer modeled and actually machined. All other bone-facing surfacesof the jig may be the result of the overestimation process such thatthese other bone-facing surfaces are spaced apart from, and do notcontact, their corresponding regions of the bone surface of thearthroplasty target region, as these bone regions correspond to regionsthat are less likely to be accurately 3D computer modeled and/or lesslikely to be actually machined. The result of the overestimatedbone-facing surfaces of the jig 2 is a jig that is more likely toaccurately and reliably matingly receive the arthroplasty target regionduring an arthroplasty procedure.

Example overestimation processes are provided below in the context ofgenerating bone-facing surfaces for a femur jig and a tibia jig, whereinsome of the bone-facing surfaces are bone mating surfaces and otherbone-facing surfaces are the result of overestimation. While thefollowing examples are provided in the context of jigs for kneearthroplasty, the overestimation process should not be considered asbeing limited to the knee context. Instead, the overestimation conceptsdisclosed herein should be considered to be applicable to all types oforthopedic surgeries by those skilled in the art, including thosesurgeries for other types of bone-to-bone interfaces such as ankle, hip,wrist, elbow, shoulder, toe, finger and other types of joints,vertebrae-to-vertebrae interfaces, vertebrae-to-hip structureinterfaces, vertebrae-to-skull interfaces, etc.

1. Overestimating the 3D Femur Surface Models

As described above with regard to block 140 of FIG. 1D, the “jig data”46 is used to produce a jigs having bone mating surfaces customized tomatingly receive the target areas 42 of the respective bones of thepatent's joint. Data for the target areas 42 may be based, at least inpart, on the 3D computer generated surface models 40 of the patient'sjoint bones. Furthermore, as described above with regard to FIG. 1A and[blocks 100-105] of FIG. 1B, these 3D computer generated surface models40 may be based on the plurality of 2D scan image slices 16 taken fromthe imaging machine 8 and, more precisely, from the contour linesderived from those 2D scan image slices via image segmentation processesknown in the art or, alternatively, as disclosed in U.S. ProvisionalPatent Application 61/126,102, which was filed Apr. 30, 2008 and isincorporated by reference herein in its entirety.

Each scan image slice 16 represents a thin slice of the desired bones.FIG. 22A illustrates the distal axial view of the 3D model of thepatient's femur shown in FIG. 5 with the contour lines 2301 of the imageslices shown and spaced apart by the thickness D_(T) of the slices. FIG.22B represents a coronal view of a 3D model of the patient's femur withthe contour lines 2301 of the image slices shown and spaced apart by thethickness D_(T) of the slices.

The slices shown in FIGS. 22A-B have contour lines 2301 similar to theopen and closed loop contour line segments 210, 210′ depicted in FIGS.2B and 2E. The contour lines 2301 of each respective image slice 16 arecompiled together to form the 3D model of the patient's femur. Theoverall resolution or preciseness of the 3D models 40 (shown in FIGS. 2Cand 2F) resulting from compiling together the contour lines of each ofthese slices (shown in [block 1010]) may be impacted by the thicknessD_(T) of the slices shown in FIGS. 22A-B. Specifically, the greater thethickness D_(T) of the slices, the lower the resolution/preciseness ofthe resulting 3D models, and the smaller the thickness D_(T) of theslices, the higher the resolution/preciseness of the resulting 3Dmodels.

As the resolution/preciseness of the 3D models increases, more accuratecustomized arthroplasty jigs 2 may be generated. Thus, the generalimpetus is to have thinner slices rather than thicker slices. However,depending upon the imaging technology used, the feasible thickness D_(T)of the image slices may vary and may be limited due a variety ofreasons. For example, an imaging thickness D_(T) that is sufficientlyprecise to provide the desired imaging resolution may also need to bebalanced with an imaging duration that is sufficiently brief to allow apatient to remain still for the entire imaging duration.

In embodiments utilizing MRI technology, the range of slice thicknessD_(T) may be from approximately 0.8 mm to approximately 5 mm. MRI slicethicknesses D_(T) below this range may be unfeasible because they haveassociated imaging durations that are too long for most patients toremain still. Also, MRI slice thicknesses D_(T) below this range may beunfeasible because they may result in higher levels of noise with regardto actual signals present, residuals left between slices, and volumeaveraging limitations of the MRI machine. MRI slice thicknesses abovethis range may not provide sufficient image resolution/preciseness. Inone embodiment, the MRI slice thicknesses D_(T) is approximately 2 mm.

While embodiments utilizing CT technology may have a range of slicethicknesses D_(T) from approximately 0.3 mm to approximately 5 mm, CTimaging may not capture the cartilage present in the patient's joints togenerate the arthritic models mentioned above.

Regardless of the imaging technology used and the resultingresolution/preciseness of the 3D models, the CNC machine 10 may beincapable of producing the customized arthroplasty jigs 2 due tomechanical limitations, especially where irregularities in the bonesurface are present. This, for example, may result where a milling toolbit has dimensions that exceed those of the feature to be milled.

FIG. 23 illustrates an example sagittal view of compiled contour linesof successive sagittal 2D MRI images based on the slices shown in FIGS.22A-B with a slice thickness D_(T) of 2 mm. As can be understood fromFIGS. 22A-23, the contour lines shown begin on the medial side of theknee at the image slice corresponding to contour line 2310 and concludeon the lateral side of the knee at the image slice corresponding tocontour line 2330. Thus, in one embodiment, contour lines 2310 and 2330represent the contour lines of the first and last images slices taken ofthe femur, with the other contour lines between contour lines 2310, 2330representing the contour lines of the intermediate image slices taken ofthe femur. Each of the contour lines is unique is size and shape, may beeither open-loop or closed-loop, and corresponds to a unique image slice16.

FIG. 24 illustrates an example contour line 2400 of one of the contourlines depicted in FIGS. 22A-23, wherein the contour line 2400 isdepicted in a sagittal view and is associated with an image slice 16 ofthe femoral condyle. As shown, the contour line 2400 includes aplurality of surface coordinate points (e.g., h−n, . . . , h−3, h−2,h−1, h, h+1, h+2, h+3, . . . , h+n; j−n, . . . , j−3, j−2, j−1, j, j+1,j+2, j+3, . . . , j+n; k−n, . . . , k−3, k−2, k−1, k, k+1, k+2, k+3, . .. , k+n; and i−n, . . . , i−3, i−2, i−1, i, i+1, i+2, i+3, . . . , i+n).The contour line and associated points may be generated by imagingtechnology, for example, via an image segmentation process that mayemploy, for example, a shape recognition process and/or a pixelintensity recognition process. In one embodiment, the contour line 2400may represent the boundary line along the cortical-cancellous bone edge.In one embodiment, the boundary line may represent the outer boundaryline of the cartilage surface.

Each of the surface contour points in the plurality may be separated bya distance “d”. In one embodiment, distance “d” may be a function of theminimum imaging resolution. In some embodiments, distance “d” may befunction of, or associated with, the size of the milling tool used tomanufacture the jig. For example, the distance “d” may be set to beapproximately 10 times smaller than the diameter of the milling tool. Inother words, the distance “d” may be set to be approximately 1/10^(th)or less of the diameter of the milling tool. In other embodiments, thedistance “d” may be in the range of between approximately one half ofthe diameter of the milling tool to approximately 1/100^(th) or less ofthe diameter of the milling tool.

Depending on the embodiment, the separation distance d may be eitheruniform along the contour line 2400, or may be non-uniform. For example,in some embodiments, areas of bone irregularities may have points thatare closer together than areas where no irregularities are present. Inone embodiment, the points shown along the example contour line 2400 mayhave a separation distance d of approximately 2 mm. In otherembodiments, distance d may be in the range of approximately 0.8 mm toapproximately 5 mm.

The bone surface of the example contour line 2400 includes a regularregion 2402A on the distal-posterior portion of the contour line 2400 aswell as an irregular region 2402B of the same. The contour line 2400also includes irregular regions 2402C-D on the distal anddistal-anterior portions, respectively. The irregular regions 2402B-Dmay be due to a variety of patient specific factors. For example,irregular region 2402B illustrates a type of bone irregularity, referredto as an “osteophyte”, where a bony outgrowth has occurred in thefemoral condyle. Osteophytes may be present in patients that haveundergone trauma to the bone or who have experienced degenerative jointdisease.

The irregular regions 2402C-D illustrate areas of the femoral condylethat have experienced cartilage damage and appear as notches in thecontour line 2400. Regardless of the cause of the irregularity, thepresence of irregularities in the contour line 2400 may adversely impactthe ability to generate a mating surface in the actual arthroplasty jigthat accurately and reliably mates with the corresponding bone surfaceof the patient during the arthroplasty procedure. This may be the resultof the imaging impreciseness in the vicinity of the contour irregularregions 2402B-D or because the contour irregular regions 2402B-Drepresent surface contours that are too small for the tooling of the CNCmachine 10 to generate. To account for contour line regions associatedwith imaging impreciseness and/or features too small to be milled viathe tooling of the CNC machine, in some embodiments, such contour lineregions may be identified and corrected or adjusted via theoverestimation process prior to being compiled to form the 3D models 40.

FIG. 25 represents an example overestimation algorithm 2500 that may beused to identify and adjust for irregular regions 2402B-D when formingthe 3D models 40. In block 2502, medical imaging may be performed on thedamaged bone at desired slice thicknesses D_(T), which in someembodiments may be equal to those slice thicknesses D_(T) mentionedabove with regard to FIGS. 22A-22B. For example, MRI and/or CT scans maybe performed at predetermined thicknesses D_(T) as shown in FIGS. 22A-B.In some embodiments, the desired thickness D_(T) used in block 2502 isset at 2 mm or any other thickness D_(T) within the range of thicknessesD_(T) mentioned above.

From this medical imaging, a series of slices 16 may be produced andimage segmentation processes can be used to generate the contour lines210, 210′, 2301, 2310, 2330, 2400 discussed with respect to FIGS. 2,22A-B, and 24 (see block 2504). Also in block 2504, a plurality ofsurface coordinate points along each contour line segment 2402A-D may beidentified as shown in FIG. 24 with respect to contour line 2400. Forexample, the points in the irregular region corresponding to contourline segment 2402B may be identified and indexed as i−n, . . . , i−1, i,i+1, i+2, i+3, . . . , i+n.

With the surface coordinate points along the contour 2400 defined, ananalysis may be performed on two or more of the points (e.g., i and i+1)to determine if an irregularity exists in the contour line segment perblock 2506.

FIG. 26 depicts implementing an example analysis scheme (according toblock 2506) on the irregular contour line region 2402B of FIG. 24. Asshown, the analysis may include constructing one or more tangent lines(labeled as t_(i−1), t_(i), t_(i+1), t_(i+2), t_(i+3), t_(i+4), etc.),corresponding to the points in the irregular region 2402B. The analysisof block 2506 may further include calculating differences between theangles formed by one or more of the tangent lines. For example, thedifference between the angles formed by the tangent lines t_(i) andt_(i+1) may be defined as w_(i), where

$w_{i} = {{\cos^{- 1}\left( \frac{t_{i + 1} \cdot t_{i}}{{t_{i + 1}}{t_{i}}} \right)}.}$In some embodiments, the operations of block 2506 may be performedrepetitively on each point within the contour segment.

The operations of block 2506 may be calculated on subsequent points(e.g., between t_(i) and t_(i+1)) in some embodiments, and onnon-subsequent points in other embodiments (e.g., t_(i+2) and t_(i+4)).

The angular difference w_(i) may indicate whether portions of thecontour line segment are too eccentric for use in constructing the 3Dmodels 40. In block 2508, the angular difference w_(i) may be comparedto a predetermined angular criterion w_(c). The angular criterion w_(c)may be determined based on several factors, including the physicaldimensions and characteristics of the CNC machine 10. In someembodiments, the predetermined angular criterion w_(c) is set atapproximately 5 degrees. In other embodiments, the predetermined angularcriterion w_(c) is set at between approximately 5 degrees andapproximately 20 degrees.

For the sake of discussing the example irregular region 2402B shown inFIG. 26, the angular criterion w_(c) is set to 5 degrees in oneembodiment. The angular differences between tangent lines associatedwith adjacent points i−2, i−1, i, i+1, i+2 are within the predeterminedangular criterion w_(c) of 5 degrees, but the differences betweentangent lines associated with adjacent points i+2 and i+3 and adjacentpoints i+3 and i+4 exceeds the predetermined angular criterion w_(c) of5 degrees and therefore indicates an irregular region of the contourline. The difference between tangent lines associated with adjacentpoints, such as i+5 and i+6, may indicate similar irregular regions. Asmentioned above, these irregularities may result from conditions of thepatient's bone such as arthritis or osteoarthritis and generally resultin a contour line segment being unsuitable for using when forming the 3Dmodels 40. Accordingly, if the comparison from block 2508 indicates thatthe angular difference w_(i) is greater than the predetermined criterionw_(c), then the data associated with the irregular contour line segmentmay be modified by overestimating (e.g., adjusting the irregular contourline segment outward or away from the bone portion of the image slice16) as discussed in greater detail below with respect to FIG. 27 (seeblock 2510).

FIG. 27 depicts the irregular region 2402B from FIG. 26 including aproposed area of overestimation, wherein an overestimation procedurecreates an adjusted contour line 2702 and positionally deviates theadjusted contour line 2702 from the original surface profile contourline 2402B. In the event that the comparison performed in block 2508indicates that the angular differences between any of the points ithrough i+14 exceed the predetermined angular criterion w_(c), then thecontour line segment may be overestimated between these points as shownby the dashed line 2702. As can be understood from a comparison ofcontour line 2402B to the overestimated or adjusted line 2702, theadjusted line 2702 is adjusted or moved outward or away from thelocation of the contour line 2402B by an offset distance. Depending onthe embodiment, the offset distance between the contour line 2402B andthe adjusted line 2702 may range between a few millimeters to a fewcentimeters. This overestimation may be built into the data used toconstruct 3D surface models 40 and result in a gap between therespective region of the bone mating surface of the jig 2 and thecorresponding portion of the patient's bone surface, thereby avoidingcontact between these respective areas of the jig and bone surface. Theother areas, such as i−1, i−2, i−3, i+15, i+16, i+17, and i+18, need notbe overestimated, per block 2510, because the differences between theirtangent lines fall within the angular difference criterion w_(c). Theseareas may be designated as potential target areas that may later be usedas the 3D surface models 40 if other angular criteria (described below)are satisfied.

By building overestimation data into the 3D surface models 40,deliberate spaces may be created in regions of the custom arthroplastyjig 2 corresponding to irregularities in the patient's bone, where it isoften difficult to predict the size and shape of these irregularitiesfrom 2D MRI or where it is difficult to accurately machine the contourline into the jig's bone mating surface because of the largeness of themilling tool relative to the changes in contour. Thus, the jig 2 mayinclude one or more deliberate spaces to accommodate theseirregularities or inability to machine. Without these deliberate spaces,the jig 2 may be potentially misaligned during the TKR surgery and mayreduce the chances of the surgery's success.

The image generation, analysis and overestimation of blocks 2506, 2508and 2510 may be performed on the other irregularities shown in FIG. 24.FIG. 28 illustrates the example analysis scheme according to algorithm2500 implemented on the irregular region 2402C where an irregularsurface of the condylar contour is observed. Akin to the analysis ofirregular region 2402B, the analysis may include constructing one ormore tangent lines (labeled as t_(j−1), t_(j), t_(j+1), t_(j+2),t_(j+3), etc.), corresponding to the points in the irregular region2402C. The analysis of block 2506 may further include calculatingdifferences between the angles formed by one or more of the tangentlines, defined as w_(j), where

$w_{j} = {\cos^{- 1}\left( \frac{t_{j + 1} \cdot t_{j}}{{t_{j + 1}}{t_{j}}} \right)}$between subsequent points t_(j) and t_(j+1). Other embodiments includeanalysis between non-subsequent points (e.g., t_(j+2) and t_(i+4)).

Akin to the analysis of irregular region 2402B, the angular differencew_(j) may indicate whether portions of the contour line segment in theirregular region 2402C are too eccentric for use in constructing the 3Dmodels 40. In block 2508, the angular difference w_(j) may be comparedto a predetermined angular criterion w_(c). If the angular criterionw_(c) is set to 5 degrees, the angular differences between adjacenttangent lines associated with j−6, j−5, j−4, j−3, j−2 and j−1 are withinthe predetermined angular criterion w_(c). The difference between j−1,j, and j+1, however, may exceed the predetermined angular criterionw_(c) of 5 degrees and therefore may indicate an irregular region of thecontour line 2400. In a similar fashion, the angular criterion w_(c) forangular differences between tangent lines associated with subsequentpoints j−6, j−7, and j−8 may indicate similar irregular regions.

As mentioned above, these irregularities may result from conditions inthe patient's bone such as arthritis or osteoarthritis and generallyresult in a contour line segment being unsuitable for using when formingthe 3D models 40. Accordingly, if the comparison from block 2508indicates that the angular difference w_(j) is greater than thepredetermined criterion w, such as the case at points j−1, j, and j+1 aswell as j−6, j−7, and j−8, then the data used in forming 3D models 40may be adjusted by the overestimating process prior to being used informing the 3D models 40.

FIG. 29A depicts the irregular region 2402C from FIG. 28 including aproposed area of overestimation indicated by the dashed line areas2902A-B, wherein the dashed line areas 2902A-B are deviated from theoriginal cortical-cancellous boundary or contour line 2402C. Since thecomparison performed in block 2508 indicates that the angular differencew, is greater than the predetermined criterion w_(c) at points j−1, j,and j+1 as well as at points j−6, j−7, and j−8, overestimation isperformed at these points (labeled as regions 2902A-B respectively). Insome embodiments to allow for an adequate transition from thenon-overestimate regions to the overestimated regions in view of thediameter of the tool to be used, the overestimation may includeadditional points to either side of the points falling outside of thepredetermined criterion w_(c) (i.e., points j−1, j, and j+1 as well asat points j−6, j−7, and j−8). Thus, the overestimation in region 2902Amay extend from j−2 through j+2, and the overestimation in region 2902Bmay extend from j−10 through j−5. Furthermore, since the comparisonperformed in block 2508 indicates that the angular difference w_(j) isless than the predetermined criterion w_(c) at points j−6, j−5, j−4,j−3, and j−2, (labeled as region 2902C) these points j−5, j−4, and j−3(adjusting for the addition of points j−6 and j−2 to the regions2902A-B) may be used in constructing the 3D models 40 as long as othercriteria (described below in the context of blocks 2514-2520) are met.

A tool 2904 may be used to form the surface of the jig's bone matingsurface from the 3D models 40 formed from the compiled contour lines,some of which may have been modified via the overestimation process. Thetool 2904 may be part of the CNC machine 10 or any other type ofmachining or manufacturing device having any type of tool or device forforming a surface in a jig blank. Regardless of the type of the deviceused to mill or form the jigs 2, the tool 2904 may have certainattributes associated with jig machining process that are taken intoaccount when performing the overestimating per block 2510. Theassociated attributes may include the accessible space for the machiningtools to reach and machine the jig's bone mating surface. Examples ofsuch attributes may include the collar diameter of the drilling cutterdevice, the allowable angle the drilling device can make with thesurface to be drilled (e.g., 45 degrees±10%), and/or the overall lengthof the drilling cutter head.

For example, if the minimum diameter of the overestimated regions2902A-B is larger than the diameter D₁ of the tool 2904, thenoverestimation of block 2510 may not need to account for the dimensionsof the tool 2904, except to provide adequate transitions leading to theoverestimated regions as illustrated above by the addition of a singleor few points (e.g., points j−2, j+2, j−5, and j−10) to either side ofthe points outside predetermined criterion w_(c).

If, on the other hand, the tool 2904 has a larger diameter D₂ as shownin the example implementation of FIG. 29B, then the overestimationperformed in block 2510 may include accounting for this larger tool sizein its overestimation. To determine if the overestimation needs to beadjusted to accommodate the larger diameter D₂, a first measurement ofthe minimum diameter of curvatures 2902A′ and 2902B′ for regions 2902A-Bmay be made. In addition, a second measurement of half of the distanceassociated with region 2902C plus the minimum diameter of curvatures2902A′ and 2902B′ for regions 2902A-B may be made. If both the first andsecond measurements are less than the diameter D₂, then the amount ofoverestimation implemented in block 2510 may be set such that theminimum curvatures of regions 2902A-B, respectively, are greater than orequal to D₂ and are increased to 2902A″ and 2902B″, respectively.Logically, this example curvature requirement may be expressed as: ifdiameter_(MIN)(2902A OR 2902B)<D₂ AND (diameter_(MIN)(2902A OR2902B)+(2902C)/2)<D₂, then overestimate so that diameter_(MIN)(2902Aand/or 2902B)≧D₂. Also, in the event that the overestimation needs toaccount for the tool diameter D₂, one or more additional points, overwhat would normally be required absent the need to account for tooldiameter, may be included such that the regions 2902A-B respectivelyextend through points j−4 through j+2 and j−12 through j−4. Thecurvatures 2902A′ and 2902B′ for the respective regions 2902A-B may befurther adjusted outward (as indicated by the arrows in FIG. 29B) to therespective diameter-accounted curvatures 2902A″ and 2902B″ to define thepotential jig mating surface for the 3D models 40. Thus, regions 2902A-Bmay increase in size to accommodate the diameter D₂ of the tool 2904 bysacrificing the area of region 2902C. It should be noted that, if addinga one or more points on either side of an overestimation region 2902A,2902B in the course of accounting for tool diameter does not result in asmooth transition into the resulting curvature 2902A″, 2902B″, thenstill further points can be added to the overestimation region until asmooth transition is achieved.

FIG. 29C shows an example implementation of the tool 2904 having an evenlarger diameter D₃ than what is shown in FIGS. 29A-B. In this scenario,if diameter_(MIN)(2902A OR 2902B)<D₃ AND (diameter_(MIN)(2902A OR2902B)+(2902C)/2)<D₃, then overestimate so thatdiameter_(MIN)(2902A-C)<D₃. As illustrated by the arrows, all threeregions 2902A-C may need to be overestimated if the size of tooldiameter is large enough, sacrificing the entirety of region 2902C tothe overestimation associated with regions 2902A-B. Thus, the initialoverestimation curvatures 2902A′ and 2902B′ end up being a singlecurvature 2902A-C″ encompassing all of regions 2902A-C. Of course,additional points can be added as needed to either side ofoverestimation region 2902A-C to provide a smooth transition into theresulting curvature 2902A-C″.

With the curves overestimated to account for factors related to the tool2904, the resulting overestimated surface profile or contour may besaved for generating the 3D model 40 as long as other criteria(described below in the context of block 2514-2520) are met.

Referring briefly back to FIG. 24, the analysis and overestimation ofalgorithm 2500 may be performed on the irregular region 2402D, where theboundary between the cortical and cancellous bone in the femoral condyleis irregular and may not be clearly identified by the imaging slices.FIG. 30 illustrates the example overestimation scheme on the irregularregion 2402D according to block 2510. As shown in FIG. 30, the irregularregion 2402D extends between points h+1 to h+10. The tangent lines (notshown in FIG. 30) of every two adjacent coordinate points shown have anangular difference greater than w_(c), and therefore, overestimation maybe performed as shown by the dashed line 3002 between points h-2 toh+13.

FIG. 31 shows a similar analysis of the regular region 2402A (from FIG.24). As was the case with the irregular regions 2402B-D, points alongthe contour line k−1 through k+4 may be identified and then tangentlines (labeled as t_(k−1), t_(k), t_(k+1), t_(k+2), t_(k+3), etc.) maybe constructed per block 2506. Per block 2508, comparing the angulardifferences w_(k) between these tangent lines using the formula

$w_{k} = {\cos^{- 1}\left( \frac{t_{k + 1} \cdot t_{k}}{{t_{k + 1}}{t_{k}}} \right)}$shows that they are within the angular criterion w_(c), which in thisexample is 5 degrees. Thus, the points shown in FIG. 31 may be saved andused as a potential surface profile for the mating surface of thefemoral jig if the surface variations between these points and points oncontour lines of adjacent slices are not too extreme. That is, if theangular differences associated with a contour line of a particular slicefall within the angular criterion w_(c), and the points are used as apotential jig surface, then surface variation between contour lines ofadjacent slices may be checked in block 2514. This approach may help toidentify certain areas where no cartilage damage or osteophyte isobserved in the imaging, yet there is a need to overestimate because thesurface variation, between the adjacent slices shown in FIGS. 22A-B, maybe too great to be used as an accurate representation of the actual bonesurface to be a potential femoral jig surface. Example areas fallingwithin this category for the femoral condyle include, the area ofanterior condylar portion close to the trochlear groove and the area ofdistal condylar portion close to the intercondylar notch to name a fewexamples.

FIG. 32A is a diagrammatic sagittal-coronal-distal isometric view ofthree contour lines 210 of three adjacent image slices 16 depictingangular relationships that may be used to determine whether portions ofthe one or more contour lines may be employed to generate 3D computermodels 40. As mentioned above, despite contour line segments and theirassociated coordinate points meeting the angular criterion w_(c) so asto not require overestimation as discussed with respect to blocks 2508and 2510, such contour line segments and associated coordinate pointsmay still require overestimation if the surface variations betweensurface contour lines 210 of adjacent imaging slices 16 is excessive.Excessive surface variation may result in volume averaging error in theregions of the 3D computer generated models corresponding to theexcessive surface variation. Jig mating surfaces based on regions of the3D computer generated models that are the result of volume averagingerror are may have difficulty accurately matingly receiving theassociated bone surfaces of the arthroplasty target region.

Such excessiveness is typically the result of variations in thepatient's knee features. For example, in the majority of cases, the areaof the anterior condylar portion close to the trochlear groove isobserved as a smooth depression. However, in other patients, a sharpedge is present in place of the smooth depression. Because of thevariation in anatomy between various patients for these varying surfaceareas and/or other varying surface areas (e.g., the area of distalcondylar portion close to the intercondylar notch), these varyingsurface areas may be generally excluded from being a potential contourline for generating a 3D model 40. In other words, such varying surfaceareas may be subjected to an overestimation process as described below.

The three contour line segments are respectively labeled in FIG. 32A asthe m^(th), m^(th+1), m^(th+2) contour line segments corresponding tothree consecutive image slices 16 spaced apart from each other by slicethickness D_(T). Each contour line includes surface contour points A-C,A′-C′ and A″-C″ that are saved for use in the potential jig surfaceprofile because, for example, the points fall within the angularcriteria discussed with respect to blocks 2506 and 2508. The points A-C,A′-C′ and A″-C″ now may be used to determine if the slice-to-slicesurface variation exceeds a predetermined threshold. For example, on them^(th) contour line in FIG. 32A, points A, B, and C may have beenidentified in blocks 2506 and 2508 as defining potential jig matingsurfaces. Similarly, in the m^(th+1) contour line in FIG. 32A, pointsA′, B′, and C′ may have been identified in blocks 2506 and 2508 asdefining potential jig mating surfaces. Likewise, in the m^(th+2)contour line in FIG. 32A, points A″, B″, and C″ may have been identifiedin blocks 2506 and 2508 as defining potential jig mating surfaces.

Because each patient's bone anatomy may be unique, changes in surfacecontour between corresponding points on contour lines of adjacent slices(i.e., from A-A′, A′-A″, B-B′, B′-B″, C-C′, or C′-C″) may be toosignificant for use as potential jig surfaces, resulting in volumeaveraging errors that may lead to surface inaccuracies for the 3Dcomputer models. As will be described in detail below with respect tothe example bone contour lines depicted in FIG. 32A, the bone surfacedefined by points A-A′-A″ may provide a potential jig mating surface,the bone surface defined by points B-B′-B″ may have too much associatednormal vector angular deviation to be used as potential jig matingsurface, and the bone surface defined by points C-C′-C″ may have toomuch associate angular deviation between corresponding points of contourlines of adjacent image slices to be used as a potential jig matingsurface.

As discussed above with respect to FIG. 24, a contour line 2400 may havea plurality of coordinate points. According to the operation of block2508 of FIG. 25, the coordinate points may fall into one of twoclassifications, namely, those coordinate points within a potential jigmating area 2402A and those coordinate points within a non-jig matingarea 2402B, 2402C and 2402D. Via the criteria of block 2514 of FIG. 25,the surface coordinate points of one contour line 2400 in potential jigmating area 2402A may be further investigated by a multi-slice (e.g.,three-slice) check. For example, coordinate point k+1 located withinarea 2402A may be coordinate point A in FIG. 32A. Similarly, coordinatepoints k and k−1 within area 2402A may be coordinate points B and C,respectively. Coordinate points A, A′ and A″ may correspond to eachother, coordinate points B, B′ and B″ may correspond to each other, andcoordinate points C, C′ and C″ may correspond to each other.Corresponding points A′, A″, B′, B″, C′, C″ for respective points A, B,C may be identified via a variety of methods, including the threemethods discussed below with respect to FIGS. 33A-33F.

Block 2514 in FIG. 25 illustrates example comparisons and/ordeterminations that may be made between corresponding points on contourlines of adjacent image slices to determine if surface variation is toogreat for the points and contour line segments to be used in generatingjig mating surfaces. The comparisons and/or determinations may involvetwo facets, which are: (1) determining the angular deviation 8 betweencorresponding coordinate points of contour lines of adjacent imageslices; and (2) comparing the angular differences φ of normal vectorsassociated with corresponding coordinate points of contour lines ofadjacent image slices. These two facets of the determination areexplained in turn below, followed by an application of these two facetsof the determination to the contours depicted in FIG. 32A.

As can be understood from FIG. 32A, in one embodiment, the comparisonsof the contour lines with respect to angular deviation 8 and angulardifferences φ may take place relative to the contour lines of threeadjacent image slices. In other embodiments, the comparisons of thecontour lines with respect to angular deviation 8 and angulardifferences φ may take place relative to the contour lines of two, fouror more adjacent image slices. In other words, depending on theembodiment, the comparison of the contour lines may be accomplished ingroups of two, three, four or more contour lines. In one embodiment, thegroups of contour lines evaluated together may be made up of adjacentcontour lines. In other embodiments, one or more of the contour lines ofa group of contour lines may not be an adjacent contour line (e.g. acontour line falling within a group may be skipped).

Where the image slices 16 are sagittal slices such as those slices 2301,2310 and 2330 depicted in FIGS. 22A-23, in one embodiment as providedbelow with respect to FIG. 32A and then again with respect to FIGS.33A-33B, corresponding coordinate points on contour lines 210 ofadjacent image slices 16 may be those coordinate points that all existin a single plane that is generally perpendicular to the sagittal imageslices. Thus, as can be understood from FIG. 32A, points A, A′ and A″may all exist in a single plane that is perpendicular to the respectiveimage slices. Line segment AA′ extends between points A and A′, and linesegment A′A″ extends between points A′ and A″. Although the linesegments AA′ and A′A″ may all exist in the same single plane that isperpendicular to the respective image slices, the line segments AA′ andA′A″ may be angularly deviated from each other such that they do notextend along a common line. This angular deviation may be the result ofeach point A, A′ and A″ being located on its respective contour linem^(th), m^(th+1), and m^(th+2) and each contour line having a differentelevation at its respective point relative to the corresponding pointson the adjacent contour lines. This elevation difference between thepoints A, A′ and A″ may be because the bone contour geometric shapechanges from contour line m^(th), m^(th+1), m^(th+2) to contour line.The order of the contour lines m^(th), m^(th+1), m^(th+2) may correspondto the order of the respective image slices, the image slice ordercorresponding to the movement of the MRI scan along the knee. Similarrelationships exist for points B, B′ and B″ and for points C, C′ and C″,resulting in similar line segments BB′, B′B″ and CC′, C′C″,respectively.

Once corresponding coordinate points are identified via the methodalready discussed above and below with respect to FIGS. 32A and 33A-33Bor via any of the methods discussed below with respect to FIGS. 33C-33F,the surface variation between adjacent contour lines may be analyzed by:(1) determining the angular deviation 8 between corresponding coordinatepoints of contour lines of adjacent image slices; and (2) comparing theangular differences φ of normal vectors associated with correspondingcoordinate points of contour lines of adjacent image slices.

As can be understood from FIG. 32A and already mentioned above, in oneembodiment, the comparisons of the contour lines with respect to angulardeviation θ and angular differences φ may take place relative to thecontour lines of three adjacent image slices. In other embodiments, thecomparisons of the contour lines with respect to angular deviation θ andangular differences φ may take place relative to the contour lines oftwo, four or more adjacent image slices. In other words, depending onthe embodiment, the comparison of the contour lines may be accomplishedin groups of two, three, four or more contour lines. In one embodiment,the groups of contour lines evaluated together may be made up ofadjacent contour lines. In other embodiments, one or more of the contourlines of a group of contour lines may not be an adjacent contour line(e.g. a contour line falling within a group may be skipped).

As can be understood from FIG. 32A, in one embodiment, the contour linesm^(th), m^(th+1), m^(th+2) may be evaluated as a group of three contourlines, wherein contour line m^(th) is compared to contour lines m^(th+1)and m^(th+2). Contour line m^(th+1) may then be compared to contourlines m^(th+2) and m^(th+3), and contour line m^(th+2) may then becompared to contour line m^(th+3) and contour line m^(th+4).Alternatively, once contour line m^(th) is compared to contour linesm^(th+1) and m^(th+2), the comparison may begin again with a comparisonof contour line m^(th+2) to contour line m^(th+3) and contour linem^(th+4). Alternatively, once contour line m^(th) is compared to contourlines m^(th+1) and m^(th+2), the comparison may begin again with acomparison of contour line m^(th+4) to contour line m^(th+5) and contourline m^(th+6). Similar orders for comparing the contour lines may beused regardless of whether the contour lines are compared in groups oftwo, four or more.

A discussion will now be given regarding the first facet of the surfacevariation analysis, namely, the determination of the angular deviation θbetween corresponding coordinate points of contour lines of adjacentimage slices per block 2514. FIG. 32B is an example right triangle 3214that may be used for determining the angular deviation θ betweencorresponding coordinate points of contour lines of adjacent imageslices per block 2514. The right triangle 3214 illustrates points A andA′ with the line segment AA′ extending between these two points. Thepoints A and A′ lie on respective contour lines m^(th) and m^(th+1). Theimage slices containing the two contour lines m^(th) and m^(th+1) areseparated by the slice thickness D_(T), which is the perpendiculardistance between the two image slices. Thus, the slice thickness D_(T)can be represented in the right triangle 3214 as the long leg of theright triangle 3214, wherein the line segment AA′ is the hypotenuse ofthe right triangle 3214. The rise or fall distance d_(AA′) between thetwo points A and A′ is a distance perpendicular to the slice thicknessD_(T) and is represented on the right triangle 3214 by the short leg ofthe right triangle 3214. The small angle θ_(AA′) of the right triangle3214 represents the angular deviation θ_(AA′) between the correspondingcoordinate points A and A′ of contour lines m^(th) and m^(th+1) ofadjacent image slices per block 2514. Thus, as can be understood fromthe triangle 3214, the angular deviation θ_(AA′) between thecorresponding coordinate points A and A′ of contour lines m^(th) andm^(th+1) of adjacent image slices may be calculated by any of thefollowing three formulas:

${\theta_{{AA}^{\prime}} = {\tan^{- 1}\left( \frac{d_{{AA}^{\prime}}}{D_{T}} \right)}};$${\theta_{{AA}^{\prime}} = {\cos^{- 1}\left( \frac{D_{T}}{{AA}^{\prime}} \right)}};{or}$$\theta_{{AA}^{\prime}} = {{\sin^{- 1}\left( \frac{d_{{AA}^{\prime}}}{{AA}^{\prime}} \right)}.}$Ideally if there were no surface variation between points A and A′, thenthe length of line segment AA′ would be equal to the slice thicknessD_(T) and the angular deviation θ_(AA′) between the correspondingcoordinate points A and A′ of contour lines m^(th) and m^(th+1) would bezero.

Determining the angular deviation θ_(AA′) between the correspondingcoordinate points A and A′ in this manner may indicate if the surfacebetween points A and A′ is too steep or varied to be used as a potentialjig mating surface. For example, the angular deviation θ between thecoordinate points may be compared to an angular criterion θ_(c), and thesurface corresponding to the coordinate points may be consideredunsuitable for the creation of the jig's bone mating surfaces where theangular deviation θ between the coordinate points is greater than theangular criterion θ_(c). Stated in the reverse and in the context ofcoordinate points A and A′, the surface corresponding to coordinatepoints A and A′ may be a potential candidate for creation of the jig'sbone mating surfaces if the angular deviation θ_(AA′) is less than theangular criterion θ_(c) (i.e., [θ_(AA′)<θ_(c)]=surface corresponding tocoordinate points A and A′ being a potential candidate for the creationof the jig's bone mating surfaces).

In one embodiment, the angular criterion θ_(c) may be approximately onedegree. However, in some embodiments, the angular criterion θ_(c) may bein the range of approximately one to approximately five degrees. Inother embodiments, the angular criterion θ_(c) may be less than orgreater than these recited values for the angular criterion θ_(c).

As can be understood from FIG. 32C, the example right triangle 3214 ofFIG. 32B can be modified to become another example right triangle 3216and used in determining the angular deviation θ_(A′A″) betweencorresponding coordinate points A′ and A″ of contour lines m^(th+1) andm^(th+2) of adjacent image slices per block 2514. The preceding threetan⁻¹, sin⁻¹ and cos⁻¹ functions may be modified to match thecircumstances of the example right triangle 3216 of FIG. 32C tocalculate the respective angular deviation θ_(A′A″). Thus, as can beunderstood from FIG. 32C, the angular deviation θ_(A′A″) between thecorresponding coordinate points A′ and A″ of contour lines m^(th+1) andm^(th+2) of adjacent image slices may be calculated by any of thefollowing three formulas:

${\theta_{A^{\prime}A^{''}} = {\tan^{- 1}\left( \frac{d_{A^{\prime}A^{''}}}{D_{T}} \right)}};$${\theta_{A^{\prime}A^{''}} = {\cos^{- 1}\left( \frac{D_{T}}{A^{\prime}A^{''}} \right)}};{or}$$\theta_{A^{\prime}A^{''}} = {{\sin^{- 1}\left( \frac{d_{A^{\prime}A^{''}}}{A^{\prime}A^{''}} \right)}.}$

As can be understood from FIGS. 32D-32G, the right triangle 3214 of FIG.32B can be similarly modified into the respective example righttriangles 3218, 3220, 3222 and 3224 of FIGS. 32D-32G, which respectivelywill facilitate the determination of the angular deviations θ_(BB′),θ_(B′B″), θ_(CC′), and θ_(C′C″) between corresponding coordinate pointsB and B′, B′ and B″, C and C′, and C′ and C″, respectively. Thepreceding three tan⁻¹, sin⁻¹ and cos⁻¹ functions may be modified tomatch the circumstances of the respective example right triangles 3218,3220, 3222 and 3224 of FIGS. 32D-32G to calculate the respective angulardeviations θ_(BB′), θ_(B′B″), θ_(CC′), and θ_(C′C″).

In a manner like that discussed with respect to the angular deviationθ_(AK) between the corresponding coordinate points A and A′, the angulardeviation θ between any of the other pairs of corresponding coordinatepoints (i.e., A′ and A″, B and B′, B′ and B″, C and C′, and C′ and C″)may be compared to an angular criterion θ_(c). Thus, where the angulardeviation θ between corresponding coordinate points exceeds the angularcriterion θ_(c), the surface associated with the coordinate points maybe considered unsuitable for use in the creation of the jig's bonemating surfaces. Stated in the reverse, the surface corresponding to thecoordinate points may be a potential candidate for creation of the jig'sbone mating surfaces if the angular deviation θ is less than the angularcriterion θ_(c) (i.e., [θ<θ_(c)]=surface corresponding to the coordinatepoints being a potential candidate for the creation of the jig's bonemating surfaces).

In one embodiment, the angular criterion θ_(c) may be approximately onedegree. However, in some embodiments, the angular criterion θ_(c) may bein the range of approximately one to approximately four degrees. Inother embodiments, the angular criterion θ_(c) may be less than orgreater than these recited values for the angular criterion θ_(c).

A discussion will now be given regarding the second facet of the surfacevariation analysis, namely, comparing the angular differences φ ofnormal vectors associated with corresponding coordinate points ofcontour lines of adjacent image slices. As indicated in FIG. 32A, eachcontour line surface coordinate point A, A′, A″, B, B′, B″, C, C′ and C″includes a respective tangent line t_(A), t_(A′), t_(A″), t_(B), t_(B′),t_(B″), t_(C), t_(C′), and t_(C″), that is parallel to the plane inwhich the associated contour line m^(th), m^(th+1) and m^(th+2) residesand tangent to the curvature of the associated contour line m^(th),m^(th+1) and m^(th+2) at the respective coordinate point A, A′, A″, B,B′, B″, C, C′ and C″. A normal vector line NV_(A), NV_(A′), NV_(A″),NV_(B), NV_(B′), NV_(B″), NV_(C), NV_(C′), and NV_(C″), extends fromeach respective coordinate point A, A′, A″, B, B′, B″, C, C′ and C″ andis perpendicular to each respective tangent line t_(A), t_(A′), t_(A″),t_(B), t_(B′), t_(B″), t_(C), t_(C′), and t_(C″). The angulardifferences φ_(A-A′) of normal vectors NV_(A) and NV_(A′) associatedwith respective corresponding coordinate points A and A′ of respectivecontour lines m^(th) and m^(th+1) may be determined with the followingformula:

$\varphi_{A - A^{\prime}} = {{\cos^{- 1}\left( \frac{{NV}_{A} \cdot {NV}_{A^{\prime}}}{{{NV}_{A}}{{NV}_{A^{\prime}}}} \right)}.}$Similarly, the angular differences φ_(A′-A″) of normal vectors NV_(A′)and NV_(A″) associated with respective corresponding coordinate pointsA′ and A″ of respective contour lines m^(th+1) and m^(th+2) may bedetermined with the following formula:

$\varphi_{A^{\prime} - A^{''}} = {{\cos^{- 1}\left( \frac{{NV}_{A^{\prime}} \cdot {NV}_{A^{''}}}{{{NV}_{A^{\prime}}}{{NV}_{A^{''}}}} \right)}.}$The angular differences φ_(B-B′) of normal vectors NV_(B) and NV_(B′)associated with respective corresponding coordinate points B and B′ ofrespective contour lines m^(th) and m^(th+1) may be determined with thefollowing formula:

$\varphi_{B - B^{\prime}} = {{\cos^{- 1}\left( \frac{{NV}_{B} \cdot {NV}_{B^{\prime}}}{{{NV}_{B}}{{NV}_{B^{\prime}}}} \right)}.}$Similarly, the angular differences φ_(B′-B″) of normal vectors NV_(B′)and NV_(B″) associated with respective corresponding coordinate pointsB′ and B″ of respective contour lines m^(th+1) and m^(th+2) may bedetermined with the following formula:

$\varphi_{B^{\prime} - B^{''}} = {{\cos^{- 1}\left( \frac{{NV}_{B^{\prime}} \cdot {NV}_{B^{''}}}{{{NV}_{B^{\prime}}}{{NV}_{B^{''}}}} \right)}.}$

The angular differences φ_(C-C′) of normal vectors NV_(C) and NV_(C′)associated with respective corresponding coordinate points C and C′ ofrespective contour lines m^(th) and m^(th+1) may be determined with thefollowing formula:

$\varphi_{C - C^{\prime}} = {{\cos^{- 1}\left( \frac{{NV}_{C} \cdot {NV}_{C^{\prime}}}{{{NV}_{C}}{{NV}_{C^{\prime}}}} \right)}.}$Similarly, the angular differences φ_(C′-C″) of normal vectors NV_(C′)and NV_(C)″ associated with respective corresponding coordinate pointsC′ and C″ of respective contour lines m^(th+1) and m^(th+2) may bedetermined with the following formula:

$\varphi_{C^{\prime} - C^{''}} = {{\cos^{- 1}\left( \frac{{NV}_{C^{\prime}} \cdot {NV}_{C^{''}}}{{{NV}_{C^{\prime}}}{{NV}_{C^{''}}}} \right)}.}$

Determining in this manner the angular differences φ of normal vectorsassociated with respective corresponding coordinate points of respectivecontour lines may indicate if the surface between the correspondingpoints is too varied to be used as a potential jig mating surface. Forexample, the angular differences φ of normal vectors associated withrespective corresponding coordinate points may be compared to an angularcriterion φ_(c), and the surface associated with the correspondingpoints may be considered unsuitable for use in the creation of the jig'sbone contacting surfaces where values for the angular differences φ aregreater than the angular criterion φ_(c). Stated in the reverse, wherethe angular differences φ of normal vectors associated with respectivecorresponding coordinate points is less than an angular criterion φ_(c),the surface corresponding to the coordinate points may be a potentialcandidate for the creation of the jig's bone mating surfaces (i.e.,φ<φ_(c)=surface corresponding to the coordinate points being a potentialcandidate for the creation of the jig's bone mating surfaces). In oneembodiment, the angular criterion φ_(c) may be approximately twodegrees. In some embodiments, the angular criterion φ_(c) may be in therange of approximately two to approximately six degrees. In otherembodiments, the angular criterion φ_(c) may be greater or less thanthese recited values for the angular criterion φ_(c).

Thus, although one or more coordinate points of a contour line maysatisfy the tangent angle criterion w_(c) of block 2508 as discussedabove with respect to FIGS. 24 and 26-31, the coordinate points maystill be inadequate for use in generating the jig's bone contactingsurfaces. This inadequateness may result from the failure of thecoordinate points to meet the criterion of block 2514, namely, thefailure of the angular deviation θ between any of the correspondingcoordinate points to meet the angular deviation criterion θ_(c) and/orthe failure of the angular differences φ of normal vectors associatedwith respective corresponding coordinate points to meet the angulardifferences criterion φ_(c). In some embodiments, when one or morecoordinate points fail to meet both the criterion θ_(c) and φ_(c) ofblock 2508, the contour lines in the locations of those failedcoordinate points may be modified via an overestimation process similarto that discussed above with respect block 2510 and FIGS. 29A-30.

In other embodiments as reflected in block 2516, when one or morecoordinate points fail to meet both the criterion θ_(c) and φ_(c) ofblock 2508, a determination may be made regarding whether or not theslice thickness D_(T) may be adjusted to a thinner slice thicknessD_(T). Reducing the slice thickness D_(T) per block 2518 may reduce thevariations between adjacent contour lines, making it more likely thatthe criterion θ_(c) and φ_(c) will be satisfied for the coordinatepoints were the entire process started over at block 2502 with a newslice thickness D_(T). If it is determined that modifying the slicethickness D_(T) would not be beneficial (e.g., due to slice thicknessD_(T) already being at a minimum because further reduction in slicethickness D_(T) may generate significant high interferences, residuals,signal-to-noise ratios and unreliable volume-averaging in the pixels),then the contour lines may be subjected to overestimation per block2510.

If the one or more coordinate points of a contour line satisfy thetangent angle criterion w_(c) of block 2508 and both of the angularcriterion θ_(c) and φ_(c) of block 2514, then such one or morecoordinate points may be recorded for the generation of the jig's bonemating surface, as indicated in block 2520 of FIG. 25. In other words,if the one or more coordinate points of a contour line satisfy thetangent angle criterion w_(c) of block 2508 and both of the angularcriterion θ_(c) and φ_(c) of block 2514, then the surfaces associatedwith such one or more coordinate points may be employed in thegeneration of corresponding bone mating surfaces of the jig, asindicated in block 2520.

An example application of the functions of block 2514 with respect tothe contour lines m^(th), m^(th+1) and m^(th+2) depicted in FIG. 32Awill now be provided. In this example, it is assumed the coordinatepoints A, A′, A″, B, B′, B″, C, C′ and C″ and their respective contourlines portions have already satisfied the tangent angle criterion w_(c)of block 2508.

As can be understood from FIGS. 32A-C, points A, A′ and A″ are in closeproximity to each other due to the close proximity of their respectivecontour line segments. The close proximity of the respective contourlines is a result of the rise or fall distances d_(AA′) and d_(A′-A″),being small at points A, A′ and A″, as the contour lines m^(th),m^(th+1) and m^(th+2) at all points A, A′, A″, B, B′, B″, C, C′ and C″are evenly spaced medially-laterally due to having equal slicethicknesses D_(T). Due to the close proximity of points A, A′ and A″,line segments AA′ and A′A″ are relatively short, resulting in angulardeviations θ_(AA′) and θ_(A′A″) that are less than the angular criterionθ_(c), which in one embodiment, may be in the range of approximately oneto approximately four degrees. As the angular deviations θ_(AA′) andθ_(A′A″) are less than the angular criterion θ_(c), the angularcriterion θ_(c) is satisfied for points A, A′ and A″, and these pointsare potential candidates for the generation of the jig's bone matingsurfaces.

As indicated in FIG. 32A, the angular differences φ_(A-A′) and φ_(A′-A″)between the normal vectors NV_(A), NV_(A′) and NV_(A″) is small,resulting in angular differences φ_(A-A′) and φ_(A′-A″) that are lessthan the angular criterion φ_(c), which in one embodiment, may be in therange of approximately two to approximately five degrees. As the angulardifferences φ_(A-A′) and φ_(A′-A″) are less than the angular criterionφ_(c), the angular criterion φ_(c) is satisfied. Because the points A,A′ and A″ have satisfied both of the angular criterion θ_(c) and φ_(c)of block 2514, the surface represented by the points A, A′ and A″ may beemployed to generate the jig's surfaces that matingly contact thepatient's arthroplasty target surfaces per block 2520.

As can be understood from FIGS. 32A and 32D-E and for reasons similar tothose discussed with respect to points A, A′ and A″, points B, B′ and B″are in close proximity to each other due to the close proximity of theirrespective contour line segments. Consequently, line segments BB′ andB′B″ are relatively short, resulting in angular deviations θ_(BB′) andθ_(B′B″) that are less than the angular criterion θ_(c). As the angulardeviations θ_(BB′) and θ_(B′B″) are less than the angular criterionθ_(c), the angular criterion θ_(c) is satisfied for points B, B′ and B″,and these points are potential candidates for the generation of thejig's bone mating surfaces.

As indicated in FIG. 32A, the angular difference φ_(B-B′) between thenormal vectors NV_(B) and NV_(B′) is small such that it is less than theangular criterion φ_(c) and, therefore, satisfies the angular criterionφ_(c). However, the angular difference φ_(B′-B″) between the normalvectors NV_(B′) and NV_(B″) is large such that it is greater than theangular criterion φ_(c) and, therefore, does not satisfy the angularcriterion φ_(c). As the points B and B′ have satisfied both of theangular criterion θ_(c) and φ_(c) of block 2514, the surface representedby the points B and B′ may be employed to generate the jig's surfacesfor matingly contacting the patient's arthroplasty target surfaces perblock 2520. However, as the points B′ and B″ have failed to satisfy bothof the angular criterion θ_(c) and φ_(c) of block 2514, the surfacerepresented by the points B′ and B″ may not be employed to generate thejig's surfaces for matingly contacting the patient's arthroplasty targetsurfaces. Instead, the slice spacing D_(T) may be evaluated per block2516 and reset per block 2518, with the process then started over atblock 2502. Alternatively, the points may be subjected to overestimationper block 2510.

As can be understood from FIGS. 32A and 32F-G and because of significantrise and fall distances d_(CC′), and d_(C′C″″) between the contour linesat points C, C′ and C″, points C, C′ and C″ are not in close proximityto each other due to the significant distance between their respectivecontour line segments. Consequently, line segments CC′ and C′C″ arerelatively long, resulting in angular deviations θ_(CC′) and θ_(C′C″)that exceed the angular criterion θ_(c) and, therefore, do not satisfythe angular criterion θ_(c).

As indicated in FIG. 32A, the angular differences φ_(C-C′) and φ_(C-C′)between the normal vectors NV_(C), NV_(C′) and NV_(C″) are small suchthat they are less than the angular criterion φ_(c) and, therefore,satisfy the angular criterion φ_(c). However, as the points C, C′ and C″do not satisfied both of the angular criterion θ_(c) and φ_(c), thesurfaces represented by the points C, C′ and C″ may not be employed togenerate the jig's surfaces for matingly contacting the patient'sarthroplasty target surfaces. Instead, the slice spacing D_(T) may beevaluated per block 2516 and reset per block 2518, with the process thenstarted over at block 2502. Alternatively, the points may be subjectedto overestimation per block 2510.

As can be understood from the preceding discussion, in one embodiment,the analysis of the contour lines may be performed slice-by-slice acrossthe series of contour lines. In other words, a first contour linem^(th+1) is compared at its respective coordinate points to thecorresponding coordinate points of the immediate neighbor contour lines(e.g., contour lines m^(th) and m^(th+2)) medial and lateral of thefirst contour line.

While the preceding example process discussed with respect to FIGS.32A-32G is given in the context of three contour lines m^(th), m^(th+1)and m^(th+2) and nine coordinate points A-C″, of course the process canbe readily applied to a greater or less number or contour lines andcoordinate points. Therefore, the process should not be interpreted asbeing limited to any number of contour lines or coordinate points.

For another example application of the functions of block 2514,reference is made to FIGS. 33A-33F. FIGS. 33A, 33C and 33E each depictportions of contour lines n^(th), n^(th+1), n^(th+2), n^(th+3) andn^(th+4) in sagittal views similar to that of FIG. 23. FIGS. 33B, 33Dand 33F each represent a bone surface contour line 3300 and a linearinterpolation bone surface contour line 3302 as viewed along sectionlines 33B-33B, 33D-33D and 33F-33F transverse to image slices containingthe contour lines n^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4) ofrespective FIGS. 33A, 33C and 33E.

As indicated in FIGS. 33A-F, contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) each include a respective coordinate point D, D′,D″, D′″ and D″″. In one embodiment, corresponding coordinate points maybe identified via the method discussed above with respect to FIG. 32A.Specifically, as can be understood from FIGS. 33A-B, correspondingcoordinate points D, D′, D″, D′″ and D″″ may be those coordinate pointsD, D′, D″, D′″ and D″″ that each exist in the same medial-lateral planethat is generally perpendicular to the sagittal image slices containingthe contour lines and coordinate points. Other groups of correspondingcoordinate points may be identified via a similar perpendicular planemethodology.

As can be understood from FIGS. 33C-D, corresponding coordinate pointsD, D′, D″, D′″ and D″″ may be identified via a second method.Specifically, the contour lines n^(th), n^(th+1), n^(th+2), n^(th+3) andn^(th+4) may be superimposed into the same image slice layer asindicated in FIG. 33D by arrow 33D1, resulting in a composite plane 33D2having a total rise or fall distance d_(DD″) between coordinate points Dand D″″. The total rise or fall distance d_(DD″″) may be the sum of therespective rise or fall distances d_(DD′), θ_(D′D″), d_(D″D′″),d_(D′″D″″) discussed below with respect to FIGS. 33B, 33C and 33F.

As indicated in FIG. 33C, the normal vector lines NV_(D), NV_(D′),NV_(D″), NV_(D′″) and NV_(D″″), the determination of which is discussedbelow with respect to FIGS. 33A, 33C and 33E, are utilized to identifythe corresponding coordinate points D, D′, D″, D′″ and D″″. For example,the normal vector line NV_(D) of coordinate point D is extended tocontour line n^(th+1), and the intersection between normal vector lineNV_(D) and contour line n^(th+1) identifies the coordinate pointcorresponding to coordinate point D, namely, coordinate point D′. Thenormal vector line NV_(D′) of coordinate point D′ is extended to contourline n^(th+2), and the intersection between normal vector line NV_(D′)and contour line n^(th+2) identifies the coordinate point correspondingto coordinate point D′, namely, coordinate point D″. The normal vectorline NV_(D″) of coordinate point D″ is extended to contour linen^(th+3), and the intersection between normal vector line NV_(D″) andcontour line n^(th+3) identifies the coordinate point corresponding tocoordinate point D″, namely, coordinate point D′″. The normal vectorline NV_(D′″) of coordinate point D′″ is extended to contour linen^(th+4), and the intersection between normal vector line NV_(D′″) andcontour line n^(th+4) identifies the coordinate point corresponding tocoordinate point D′″, namely, coordinate point D″″. Other groups ofcorresponding coordinate points may be identified via a normal vectorline methodology.

As can be understood from FIGS. 33F-E, corresponding coordinate pointsD, D′, D″, D′″ and D″″ may be identified via a third method.Specifically, the contour lines n^(th), n^(th+1), n^(th+2), n^(th+3) andn^(th+4) may be superimposed into the same image slice layer asindicated in FIG. 33F by arrow 33D1, resulting in a composite plane 33D2having a total rise or fall distance d_(DD″″) between coordinate pointsD and D″″. The total rise or fall distance d_(DD″″) may be the sum ofthe respective rise or fall distances d_(DD′), d_(D′D″), d_(D″D′″),d_(D′″D″″) discussed below with respect to FIGS. 33B, 33C and 33F.

As indicated in FIG. 33E, a center point CP is identified. The centerpoint CP may generally correspond to an axis extending generallyperpendicular to the sagittal image slices. The center point CP may beconsidered to be a center point generally common to the curvature of allof the contour lines n^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4)and about which all of the contour lines n^(th), n^(th+1), n^(th+2),n^(th+3) and n^(th+4) arcuately extend.

As shown in FIG. 33E, radius lines R, R′, R″, etc. may radially extendin a straight line from the center point CP across the contour linesn^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4). As can be understoodfrom radius line R, the corresponding coordinate lines D, D′, D″, D′″and D″″ are identified where radius line R intersects each respectivecontour lines n^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4). Othergroups of corresponding coordinate points may be identified with radiuslines R′, R″ and etc.

Once the corresponding coordinate points D, D′, D″, D′″ and D″″ areidentified via any of the three methods, the extent of the surfacevariation between the corresponding coordinate points D, D′, D″, D′″ andD″″ may be analyzed as follows.

As can be understood from FIGS. 33A-F, each coordinate point D, D′, D″,D′″ and D″″ includes a respective tangent line t_(D), t_(D′), t_(D″),t_(D′″) and t_(D″″) that is tangent to the corresponding contour linen^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4) at the coordinatepoint D, D′, D″, D′″ and D″″, each tangent line t_(D), t_(D′), t_(D″),t_(D′″) and t_(D″″) being parallel to and contained within the imageslice of its contour line. A vector line NV_(D), NV_(D′) and NV_(D″),NV_(D′″), and NV_(D″″) extends normally from each respective tangentline t_(D), t_(D′), t_(D″), t_(D′″) and t_(D″″) at each respectivecoordinate point D, D′, D″, D′″ and D″″. Line segments DD′, D′D″, D″D′″and D′″D″″ extend between their associated coordinate points to create alinear interpolation 3302 of the bone contour line 3300.

In this example, it is assumed the coordinate points D, D′, D″, D′″ andD″″ and their respective contour lines portions have already satisfiedthe tangent angle criterion w_(c) of block 2508. For example, point Dmay be point k of potential mating region 2402A of contour line 2400 inFIG. 24, and coordinate points D′-D″″ may be points on contour lines ofadjacent image slices, wherein coordinate points D′-D″″ are identifiedas coordinate points corresponding to coordinate point D. Each of thecoordinate points D, D′, D″, D′″ and D″″ is then evaluated to determineif the criterion of θ_(c) and φ_(c) of block 2514 are satisfied too.

As can be understood from FIGS. 33B, 33D and 33F, points D″, D′″ and D″″are in close proximity to each other due to the close proximity of theirrespective contour line segments. The close proximity of the respectivecontour lines is a result of the rise or fall distances d_(D′″D′″) andd_(D′″D″″) being small at points D″, D′″ and D″″, as the contour linesn^(th), n^(th+1), n^(th+2), n^(th+3) and n^(th+4) at all points D, D′,D″, D′″ and D″″ are evenly spaced medially-laterally due to having equalslice thicknesses D_(T), which, for example, may be a slice thicknessD_(T) of 2 mm. Due to the close proximity of points D″, D′″ and D″″,line segments D″D′″ and D′″D″″ range in size from relatively short tonearly zero, resulting in angular deviations θ_(D″D′″) and θ_(D′″D″″)that are less than the angular criterion θ_(c), which in one embodiment,may be in the range of approximately one to approximately four degrees.As the angular deviations θ_(D″D′″) and θ_(D′″D″″) are less than theangular criterion θ_(c), the angular criterion θ_(c) is satisfied forpoints D″, D′″ and D″″, and these points are potential candidates forthe generation of the jig's bone mating surfaces. As can be understoodfrom FIGS. 33B, 33D and 33F, the angular deviations θ_(D″D′″) andθ_(D′″D″″) being less than the angular criterion θ_(c) results in thecorresponding line segments D″D′″ and D′″D″″ closely approximating thecontour of the bone surface 3300.

As indicated in FIGS. 33A, 33C and 33E, the angular differencesφ_(D″-D′″) and φ_(D′″-D″″) between the normal vectors NV_(D″), NV_(D′″)and NV_(D″″) is small, resulting in angular differences φ_(D″-D′″) andφ_(D′″-D″″) that are less than the angular criterion φ_(c), which in oneembodiment, may be in the range of approximately two to approximatelyfive degrees. As the angular differences φ_(D″-D′″) and φ_(D′″-D″″) areless than the angular criterion φ_(c), the angular criterion φ_(c) issatisfied. As can be understood from the tangent lines t_(D″), t_(D′″)and t_(D″″) depicted in FIGS. 33A, 33C and 33E, the contour line slopesat the respective coordinate points D″, D′″ and D″″ are nearlyidentical, indicating that there is little surface variation between thecoordinate points and the coordinate points would be a closeapproximation of the actual bone surface.

Because the points D″, D′″ and D″″ have satisfied both of the angularcriterion θ_(c) and φ_(c) of block 2514, the surface represented by thepoints D″, D′″ and D″″ may be employed to generate the jig's surfacesthat matingly contact the patient's arthroplasty target surfaces perblock 2520.

As can be understood from FIGS. 33B, 33D and 33F and because ofsignificant rise and fall distances d_(DD′) and d_(D′D″) between thecontour lines at points D, D′ and D″, points D, D′ and D″ are not inclose proximity to each other due to the significant distance betweentheir respective contour line segments. Consequently, line segments DD′and D′D″ are relatively long, resulting in angular deviations θ_(DD′)and θ_(D′D″) that exceed the angular criterion θ_(c) and, therefore, donot satisfy the angular criterion θ_(c). As the angular deviationsθ_(D″D′″) and θ_(D′″D″″) are greater than the angular criterion θ_(c),the angular criterion θ_(c) is not satisfied for points D, D′ and D″,and these points are not potential candidates for the generation of thejig's bone mating surfaces. As can be understood from FIGS. 33B, 33D and33F, the angular deviations θ_(DD′) and θ_(D′D″) being greater than theangular criterion θ_(c) results in the corresponding line segments DD′and D′D″ not closely approximating the contour of the bone surface 3300.

As indicated in FIGS. 33A, 33C and 33E, the angular differences φ_(D-D′)and φ_(D′-D″) between the normal vectors NV_(D) and NV_(D′) and NV_(D′)and NV_(D″) are large such that they are greater than the angularcriterion φ_(c) and, therefore, do not satisfy the angular criterionφ_(c). Thus, as the points D, D′ and D″ do not satisfied both of theangular criterion θ_(c) and φ_(c), the surfaces represented by thepoints D, D′ and D″ may not be employed to generate the jig's surfacesfor matingly contacting the patient's arthroplasty target surfaces.Instead, the slice spacing D_(T) may be evaluated per block 2516 andreset per block 2518, with the process then started over at block 2502.Alternatively, the points may be subjected to overestimation per block2510.

FIG. 34 is a distal view similar to that of FIGS. 5 and 22A depictingcontour lines 3400 produced by imaging the right femur at an imagespacing D_(T) of, for example, 2 mm. As shown, the contour lines 3400may be grouped into multiple regions in the lateral-medial direction3402-3408 for the sake of discussion. The region 3402 includes thecontour lines 3400 of the most lateral half of the femoral lateralcondyle and extends medially from the most lateral side of the femorallateral condyle to the medial-lateral middle of the femoral lateralcondyle. The region 3404 includes the contour lines 3400 of the mostmedial half of the femoral lateral condyle and extends medially from themiddle of the femoral lateral condyle to the medial-lateral center ofintercondylar notch. The region 3406 includes the contour lines 3400 ofthe most lateral half of the femoral medial condyle and extends mediallyfrom the medial-lateral center of the intercondylar notch to themedial-lateral middle of the femoral medial condyle. The region 3408includes the contour lines 3400 of the most medial half of the femoralmedial condyle and extends medially from the medial-lateral middle ofthe femoral medial condyle to the most medial side of the femoral medialcondyle.

FIG. 35 is a sagittal view of the contour lines 3400 of region 3402 ofFIG. 34. The contour lines 3400 of region 3402 include contour lines3502, 3503, 3504, 3505, 3506, 3507 and 3508, with the most lateralportion of the femoral lateral condyle being indicated by contour line3502. The size of each successive contour line 3400 of region 3402increases moving medially from the most lateral contour line 3502 ofregion 3402 to the most medial contour line 3508 of region 3402, whichis near the medial-lateral middle of the lateral condyle.

As can be understood from FIG. 35, the contour lines 3502-3504 arespaced apart from their respective adjacent contour lines a substantialamount around their entire boarders. Such wide spacing corresponds to asubstantial amount of rise or fall distances between adjacent contourlines, as discussed above with respect to FIG. 33B. Thus, such contourlines would likely fail to meet the angular criterion θ_(c) and besubject to the overestimation process such that jig surfacescorresponding to the contour lines 3502-3504 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 35, in the distal portion of the femoralcondyle, the contour lines 3505-3508 in the region 3510 converge suchthat there is little, if any, amount of rise or fall distance betweenadjacent contour lines. Thus, such contour lines 3505-3508 in the region3510 would likely meet the first angular criterion θ_(c).

As can be understood from the arrows in region 3510, the angulardifferences between normal vectors for the contour line portions withinthe region 3510 would be minimal, likely meeting the second angularcriterion φ_(c). Thus, as the portions of the contour lines 3505-3508within region 3510 likely meet both angular criterion θ_(c) and φ_(c),the portions of the contour lines 3505-3508 within the region 3510represent an optimal contact area 3510 for mating contact with the jig'sbone mating surface 40. In one embodiment, as can be understood fromFIG. 39A discussed below, the optimal contact area 3510 may be thelateral half of the surface of the lateral condyle that displacesagainst the recess of the lateral tibia plateau.

In one embodiment, the optimal contact area 3510 matingly corresponds tothe jig's bone mating surface 40 such that the portions of the contourlines 3402 indicated by region 3510 may be used to generate the jig'sbone mating surface 40, per the algorithm 2500 of FIG. 25. Conversely,per the algorithm 2500, the portions of the contour lines 3402 outsideregion 3510 may be subjected to the overestimation process discussedabove such that the jig's surfaces created from the overestimatedcontour line portions results in jig surfaces that do not contact thecorresponding portions of the patient's arthroplasty target regions.

FIG. 36 is a sagittal view of the contour lines 3400 of region 3404 ofFIG. 34. The contour lines 3400 of region 3404 include contour lines3602, 3603, 3604, 3605, 3606, 3607, 3608, 3609 and 3610 with the mostlateral portion of region 3404 being indicated by contour line 3602,which is near the medial-lateral middle of the lateral condyle, and themost medial portion of region 3404 being indicated by contour line 3610,which is near the medial-lateral center of intercondylar notch. The sizeof each successive contour line 3400 of region 3404 decreases movingmedially from the most lateral contour line 3602 to the most medialcontour line 3610.

As can be understood from FIG. 36, the contour lines 3607-3610 arespaced apart from their respective adjacent contour lines a substantialamount in their posterior portions and to a lesser extent in theirdistal portions, these distal portions corresponding to theintercondylar notch and trochlear groove. Such wide spacing correspondsto a substantial amount of rise or fall distances between adjacentcontour lines, as discussed above with respect to FIG. 33B. Thus, suchcontour lines would likely fail to meet the angular criterion θ_(c) andbe subject to the overestimation process such that jig surfacescorresponding to the contour lines 3607-3610 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 36, in the distal portion of the femoralcondyle, the contour lines 3602-3606 in the region 3614 converge suchthat there is little, if any, amount of rise or fall distance betweenadjacent contour lines. Similarly, in the anterior condylar portion ofthe distal femur, the contour lines 3602-3606 in the region 3616converge such that there is little, if any, amount of rise or falldistance between adjacent contour lines. Thus, such contour lines3602-3606 in the regions 3614 and 3616 would likely meet the firstangular criterion θ_(c).

As can be understood from the arrows in regions 3614 and 3616, theangular differences between normal vectors for the contour line portionswithin the regions 3614 and 3616 would be minimal, likely meeting thesecond angular criterion φ_(c). Thus, as the portions of the contourlines 3602-3606 within regions 3614 and 3616 likely meet both angularcriterion θ_(c) and φ_(c), the portions of the contour lines 3602-3606within the regions 3614 and 3616 represent optimal contact areas 3614and 3616 for mating contact with the jig's bone mating surface 40.

In one embodiment, the optimal contact areas 3614 and 3616 matinglycorrespond to the jig's bone mating surface 40 such that the portions ofthe contour lines 3404 indicated by regions 3614 and 3616 may be used togenerate the jig's bone mating surface 40, per the algorithm 2500 ofFIG. 25. Conversely, per the algorithm 2500, the portions of the contourlines 3404 outside regions 3614 and 3616 may be subjected to theoverestimation process discussed above such that the jig's surfacescreated from the overestimated contour line portions results in jigsurfaces that do not contact the corresponding portions of the patient'sarthroplasty target regions.

In one embodiment, as can be understood from FIG. 39A discussed below,the optimal contact area 3614 may be the medial half of the surface ofthe lateral condyle that displaces against the recess of the lateraltibia plateau. In one embodiment, as can be understood from FIG. 39Adiscussed below, the optimal contact area 3616 may be the lateral halfof a generally flat surface of the anterior condyle, wherein the flatsurface is located in an area proximal the concave trochlear groove ofthe patellar face and extends to a point near the anterior portion ofthe femoral shaft.

FIG. 37 is a sagittal view of the contour lines 3400 of region 3406 ofFIG. 34. The contour lines 3400 of region 3406 include contour lines3702, 3703, 3704, 3705, 3706, 3707, 3708, 3709 and 3710 with the mostlateral portion of region 3404 being indicated by contour line 3702,which is near the medial-lateral center of intercondylar notch, and themost medial portion of region 3406 being indicated by contour line 3710,which is near the medial-lateral middle of the medial condyle. The sizeof each successive contour line 3400 of region 3406 increases movingmedially from the most lateral contour line 3702 to the most medialcontour line 3710.

As can be understood from FIG. 37, the contour lines 3702-3706 arespaced apart from their respective adjacent contour lines a substantialamount in their posterior portions and to a lesser extent in theirdistal portions, these distal portions corresponding to theintercondylar notch and trochlear groove. Such wide spacing correspondsto a substantial amount of rise or fall distances between adjacentcontour lines, as discussed above with respect to FIG. 33B. Thus, suchcontour lines would likely fail to meet the angular criterion θ_(c) andbe subject to the overestimation process such that jig surfacescorresponding to the contour lines 3607-3610 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 37, in the distal portion of the femoralcondyle, the contour lines 3707-3710 in the region 3714 converge suchthat there is little, if any, amount of rise or fall distance betweenadjacent contour lines. Similarly, in the anterior condylar portion ofthe distal femur, the contour lines 3707-3710 in the region 3716converge such that there is little, if any, amount of rise or falldistance between adjacent contour lines. Thus, such contour lines3707-3710 in the regions 3714 and 3716 would likely meet the firstangular criterion θ_(c).

As can be understood from the arrows in regions 3714 and 3716, theangular differences between normal vectors for the contour line portionswithin the regions 3714 and 3716 would be minimal, likely meeting thesecond angular criterion φ_(c). Thus, as the portions of the contourlines 3707-3710 within regions 3714 and 3716 likely meet both angularcriterion θ_(c) and φ_(c), the portions of the contour lines 3707-3710within the regions 3714 and 3716 represent optimal contact areas 3714and 3716 for mating contact with the jig's bone mating surface 40.

In one embodiment, the optimal contact areas 3714 and 3716 matinglycorrespond to the jig's bone mating surface 40 such that the portions ofthe contour lines 3406 indicated by regions 3714 and 3716 may be used togenerate the jig's bone mating surface 40, per the algorithm 2500 ofFIG. 25. Conversely, per the algorithm 2500, the portions of the contourlines 3406 outside regions 3714 and 3716 may be subjected to theoverestimation process discussed above such that the jig's surfacescreated from the overestimated contour line portions results in jigsurfaces that do not contact the corresponding portions of the patient'sarthroplasty target regions.

In one embodiment, as can be understood from FIG. 39A discussed below,the optimal contact area 3714 may be the lateral half of the surface ofthe medial condyle that displaces against the recess of the medial tibiaplateau. In one embodiment, as can be understood from FIG. 39A discussedbelow, the optimal contact area 3716 may be the medial half of agenerally flat surface of the anterior condyle, wherein the flat surfaceis located in an area proximal the concave trochlear groove of thepatellar face and extends to a point near the anterior portion of thefemoral shaft.

FIG. 38 is a sagittal view of the contour lines 3400 of region 3408 ofFIG. 34. The contour lines 3400 of region 3408 include contour lines3802, 3803, 3804, 3805, 3806, 3807, 3808, 3809, 3810, 3811 and 3812,with the most medial portion of the femoral lateral condyle beingindicated by contour line 3812. The size of each successive contour line3400 of region 3408 decreases moving medially from the most lateralcontour line 3802 of region 3408, which is near the medial-lateralmiddle of the medial condyle, to the most medial contour line 3812 ofregion 3408.

As can be understood from FIG. 38, the contour lines 3810-3812 arespaced apart from their respective adjacent contour lines a substantialamount around their entire boarders. Such wide spacing corresponds to asubstantial amount of rise or fall distances between adjacent contourlines, as discussed above with respect to FIG. 33B. Thus, such contourlines would likely fail to meet the angular criterion θ_(c) and besubject to the overestimation process such that jig surfacescorresponding to the contour lines 3810-3812 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 38, in the distal portion of the femoralcondyle, the contour lines 3802-3809 in the region 3814 converge suchthat there is little, if any, amount of rise or fall distance betweenadjacent contour lines. Thus, such contour lines 3802-3809 in the region3814 would likely meet the first angular criterion θ_(c).

As can be understood from the arrows in region 3814, the angulardifferences between normal vectors for the contour line portions withinthe region 3814 would be minimal, likely meeting the second angularcriterion φ_(c). Thus, as the portions of the contour lines 3802-3809within region 3814 likely meet both angular criterion θ_(c) and φ_(c),the portions of the contour lines 3802-3809 within the region 3814represent an optimal contact area 3814 for mating contact with the jig'sbone mating surface 40. In one embodiment, as can be understood fromFIG. 39A discussed below, the optimal contact area 3814 may be themedial half of the surface of the medial condyle that displaces againstthe recess of the medial tibia plateau.

In one embodiment, the optimal contact area 3814 matingly corresponds tothe jig's bone mating surface 40 such that the portions of the contourlines 3408 indicated by region 3814 may be used to generate the jig'sbone mating surface 40, per the algorithm 2500 of FIG. 25. Conversely,per the algorithm 2500, the portions of the contour lines 3408 outsideregion 3814 may be subjected to the overestimation process discussedabove such that the jig's surfaces created from the overestimatedcontour line portions results in jig surfaces that do not contact thecorresponding portions of the patient's arthroplasty target regions.

As can be understood from the preceding discussion, the overestimationprocess disclosed herein can be used to identifying optimal target areas(e.g., optimal target areas 3510, 3614, 3616, 3714, 3716 and 3814 asdiscussed with respect to FIGS. 35-38). More specifically, theoverestimation process disclosed herein can employ these optimal targetareas to generate the bone mating surfaces 40 of the jigs 2 whilecausing the other surface areas of the jigs to be configured such thatthese other jig surface areas will not contact the surfaces of thearthroplasty target areas when the jig's bone mating surfaces 40 havematingly received and contacted the arthroplasty target areas. Theresult is a jig that has bone mating surfaces 40 that are based on theregions of the arthroplasty target region that are most accuratelyrepresented via 3D computer modeling and most likely to be machinableinto the jig. Such a jig provides an increased accuracy of fit betweenthe jig's mating surface 40 and the arthroplasty target areas of thepatient's bone.

For most patients, it is common that the overestimation process outlinedin FIG. 25 will result in certain areas of the femoral arthroplastytarget region being identified as the optimal target areas discussedabove with respect to FIGS. 35-38. For example, as depicted in FIG. 39A,which is distal-sagittal isometric view of a femoral distal end 3900, acommonly encountered, healthy, non-deformed femoral distal end 3900 mayhave an arthroplasty target region 3902 with certain optimal targetregions 3904, 3906 and 3908. These optimal target regions 3904, 3906 and3908 commonly identified on most patients via the overestimation processof FIG. 25 are indicated in FIG. 39A by the cross-hatched regions. Ithas been found that these optimal target regions 3904, 3906 and 3908 arethe regions of the arthroplasty target region 3902 that are most likelyto satisfy the criterion w_(i), θ_(c) and φ_(c) of blocks 2508 and 2514of FIG. 25. Therefore, these target regions 3904, 3906 and 3908 may beused to generate the jig's bone mating surfaces 40.

While, in one embodiment, the overestimation process of FIG. 25 islikely to result in optimal target regions such as those indicated viathe cross-hatching 3904, 3906 and 3908, in other embodiments, theoptimal target regions may result in target regions in other locationson the femoral distal end 3900 that are in addition to, or in place of,those regions 3904, 3906 and 3908 depicted in FIG. 39A.

One of the benefits of the overestimation process of FIG. 25 is that itidentifies two types of contour lines 210, the first type being thosecontour lines that are most likely to be unacceptable for the generationa jig's bone mating surfaces 40, and the second type being those contourlines that are most likely to be acceptable for the generation of ajig's bone mating surfaces 40. The first type of contour lines areunlikely to be acceptable for the generation of a jig's bone matingsurfaces 40 because they pertain to bone surfaces that are too varied tobe accurately 3D computer modeled and/or are such that they are notreadily machinable into the jig blank. Conversely, the second type ofcontour lines are likely to be acceptable for the generation of a jig'sbone mating surfaces 40 because they pertain to bone surfaces that varysuch an insubstantial amount that they can be accurately 3D computermodeled and are such that they are readily machinable into the jigblank. While optimal target regions 3904, 3906 and 3908 representregions likely corresponding to contour lines of the second type formost commonly encountered patients, the overestimation processesdisclosed herein may be adapted to result in other or additional optimaltarget regions.

In some instances the entirety of the target regions 3904, 3906 and 3908may correspond to the second type of contour lines, namely those type ofcontour lines that satisfy the criterion w_(i), θ_(c) and φ_(c) ofblocks 2508 and 2514 of FIG. 25. In such instances, the entirety of thetarget regions 3904, 3906 and 3908 are matingly contacted by the jig'sbone mating surface 40.

However, in some instances one or more potions of one or more of thetarget regions 3904, 3906 and 3908 may be subjected to overestimation sothat the jig's bone mating surface 40 does not contact such portions ofthe target regions 3904, 3906 and 3908, although the jig's bone matingsurface 40 still matingly contacts the other portions of the targetregions 3904, 3906 and 3908 corresponding to the second type of contourlines. Such a situation may arise, for example, where a substantialsurface variation (e.g., a hole, deformity or osteophyte) exists on acondyle articular surface 3918, 3919 that meets the criterion w_(i),θ_(c) and φ_(c) of blocks 2508 and 2514 for the rest of its surface.

The overestimation process disclosed herein may result in theidentification of target regions 3904, 3906, 3908 that are most likelyto result in bone mating surfaces 40 of jigs 2 that are readilymachinable into the jigs 2 and most likely to facilitate reliable andaccurate mating of the jigs to the arthroplasty target regions. Theoverestimation process results in such accurate and reliable bone matingsurfaces 40 while causing other surfaces of the jigs 2 corresponding toless predictable bone surfaces to not contact the bone surfaces when thebone mating surfaces 40 matingly receive the target regions 3904, 3906,3908 of the actual arthroplasty target region.

As indicated in FIG. 39A by the cross-hatched regions, optimal targetregions 3904, 3906 and 3908 may include three general areas of thefemoral condyle 3910. For example, the anterior optimal target region3904 may include the anterior portion of the femoral distal end 3900just proximal of the condyle 3910 region, the lateral optimal targetregion 3906 may include the distal portion of the lateral condyle 3912,and the medial optimal target region 3908 may include the distal portionof the medial condyle 3914.

As indicated in FIG. 39A, the femoral distal end 3900 may include alateral condyle 3912 and a lateral epicondyle 3913, a medial condyle3914 and a medial epicondyle 3915, a intercondylar notch 3939 and atrochlear groove 3916 of the patellar surface separating the twocondyles 3912 and 3914, and a femoral shaft 3917 extending distally fromthe condyle region 3910. Each condyle 3912 and 3914 includes anarticular surface 3918 and 3919 that articulates against correspondingarticular surfaces of the tibia plateau.

As indicated in FIG. 39D, which is a coronal view of the anterior sideof the femoral distal end 3900, the articular surfaces of the condyles3914, 3912 and the trochlear groove 3916 transition into each other toform a patellar facet 39D1 that has an anterior boarder or seam 39D2.Proximal of the patellar facet boarder 39D2 and identified by a dashedline is the capsular line 39D3 extending medial-lateral in an arc. Theadductor tubercle is indicated at 39D4, the fibular lateral ligament at39D5, the popliteus at 39D6, the vastus intermedius at 39D7, and thearticular genu at 39D8.

As indicated in FIG. 39A by the cross-hatching, in one embodiment, thelateral optimal target region 3906 may be generally coextensive with thelateral condyle articular surface 3918 that articulates against therespective articulate surface of the tibia plateau. In one embodiment,the lateral optimal target region 3906 may extend: anterior-posteriorbetween the anterior end 3920 and posterior end 3921 of the lateralarticular condyle surface 3918; and lateral-medial between the lateralside 3922 and medial side 3923 of the lateral articular condyle surface3918. In one embodiment, the lateral optimal target region 3906generally begins near the anterior-distal end 3920 of the lateralcondyle 3912 outside the trochlear groove 3916 of the patellar surfaceand ends near the posterior-distal end 3921 of the lateral condyle 3912.In one embodiment as can be understood from FIG. 39A, the lateraloptimal target region 3906 may be the entire cross-hatched region 3906or any one or more portions of the cross-hatched region 3906.

In one embodiment as indicated in FIG. 39A by the double cross-hatching,an anterior target area 3906A and a distal target area 3906D may beidentified within the lateral optimal target region 3906 via theoverestimation process disclosed herein. Thus, although the lateraloptimal target region 3906 may be generally coextensive with the lateralcondyle articular surface 3918, the actual areas within the lateraloptimal target region 3906 identified as being reliable surfaces for thegeneration of the mating surfaces of arthroplasty jigs may be limited toan anterior target area 3906A and a distal target area 3906D, theremainder of the lateral optimal target region 3906 being subjected tothe overestimation process. The anterior target area 3906A may belocated in the anterior third of the lateral optimal target region 3906,and the distal target area 3906D may be located near a most distal pointof the lateral optimal target region 3906.

As indicated in FIG. 39A by the cross-hatching, in one embodiment, themedial optimal target region 3908 may be generally coextensive with themedial condyle articular surface 3919 that articulates against therespective articulate surface of the tibia plateau. Specifically, in oneembodiment, the medial optimal target region 3908 may extend:anterior-posterior between the anterior end 3924 and posterior end 3925of the medial articular condyle surface 3919; and lateral-medial betweenthe lateral side 3926 and medial side 3927 of the medial articularcondyle surface 3919. In one embodiment, the medial optimal targetregion 3908 generally begins near the anterior-distal end 3924 of themedial condyle 3914 outside the trochlear groove 3916 of the patellarsurface and ends near the posterior-distal end 3925 of the medialcondyle 3914. In one embodiment as can be understood from FIG. 39A, themedial optimal target region 3908 may be the entire cross-hatched region3908 or any one or more portions of the cross-hatched region 3908.

In one embodiment as indicated in FIG. 39A by the double cross-hatching,an anterior target area 3908A and a distal target area 3908D may beidentified within the medial optimal target region 3908 via theoverestimation process disclosed herein. Thus, although the medialoptimal target region 3908 may be generally coextensive with the medialcondyle articular surface 3919, the actual areas within the medialoptimal target region 3908 identified as being reliable surfaces for thegeneration of the mating surfaces of arthroplasty jigs may be limited toan anterior target area 3908A and a distal target area 3908D, theremainder of the medial optimal target region 3908 being subjected tothe overestimation process. The anterior target area 3908A may belocated in the anterior third of the medial optimal target region 3908,and the distal target area 3908D may be located near a most distal pointof the medial optimal target region 3908.

As indicated in FIG. 39A by the cross-hatching, in one embodiment, theanterior optimal target region 3904 may be a generally planar area ofthe anterior side of the femoral shaft 3917 proximally adjacent thecondyle portion 3910 of the femoral distal end 3900. In other words, theanterior optimal target region 3904 may be a generally planar area ofthe anterior side of the femoral shaft 3917 proximally adjacent theanterior end 3940 of the trochlear groove 3916.

As shown in FIG. 39D by the cross-hatching, in one embodiment, theanterior optimal target region 3904 may be located in a generally planarsurface region of the anterior side of the femoral shaft 3917 generallydistal of the articularis genu 39D8 and generally proximal of thepatellar facet boarder 39D2. In one embodiment, the anterior optimaltarget region 3904 may be located in a generally planar surface regionof the anterior side of the femoral shaft 3917 generally distal of thearticularis genu 39D8 and generally proximal of the capsular line 39D3.In either case, the anterior optimal target region 3904 may be generallycentered medial-lateral on the anterior side of the femoral shaft 3917.

As can be understood from FIG. 39A, in one embodiment, the anteriortarget region 3904 may have a lateral-medial dimension of approximatelyone centimeter to approximately seven centimeters. In one embodiment,the anterior optimal target region 3904 may be approximately centered ona line that: is generally parallel to the femoral anatomical axis; andextends from the center of the trochlear groove 3916. In one embodiment,the medial-lateral width of the anterior optimal target region 3904 maybe medially-laterally bounded by lines extending generally parallel tothe femoral anatomical axis from the most medial and most lateralboundaries of the trochlear groove 3916. In one embodiment as can beunderstood from FIG. 39A, the anterior target region 3904 may be theentire cross-hatched region 3904 or any one or more portions of thecross-hatched region 3904.

In one embodiment as indicated in FIGS. 39A and 39D by the doublecross-hatching, an anterior target area 3904A may be identified withinthe anterior optimal target region 3904 via the overestimation processdisclosed herein. Thus, although the anterior optimal target region 3904may be generally coextensive with the generally planar surface areabetween the articularis genu 39D8 and the capsular line 39D3, the actualareas within the anterior optimal target region 3904 identified as beinga reliable surface for the generation of the mating surfaces ofarthroplasty jigs may be limited to an anterior target area 3904A, theremainder of the anterior optimal target region 3904 being subjected tothe overestimation process. The anterior target area 3904A may belocated any where within the anterior optimal target region 3904.

FIG. 39B is bottom perspective view of an example customizedarthroplasty femoral jig 2A that has been generated via theoverestimation process disclosed herein. Similar to the femoral jig 2Adepicted in FIGS. 1G and 1F, the femoral jig 2A of FIG. 39B includes aninterior or bone-facing side 100 and an exterior side 102. When the jig2A is mounted on the arthroplasty target region during a surgicalprocedure, the bone-facing side 100 faces the surface of thearthroplasty target region while the exterior side 102 faces in theopposite direction.

The interior or bone-facing side 100 of the femur cutting jig 2Aincludes bone mating surfaces 40-3904, 40-3906 and 40-3908 that: aremachined into the jig interior or bone-facing side 100 based on contourlines that met the criterion of blocks 2508 and 2514 of FIG. 25; andrespectively correspond to the optimal target regions 3904, 3906 and3908 of FIG. 39A. The rest 100′ of the interior or bone-facing side 100(i.e., the regions 100′ of the interior or bone facing sides 100 outsidethe bounds of bone mating surfaces 40-3904, 40-3906 and 40-3908) are theresult of the overestimation process wherein the corresponding contourlines failed to meet one or more of the criterion of blocks 2508 and2514 of FIG. 25 and, consequently, were moved away from the bonesurface. As a result, the interior side surface 100′ is machined to bespaced away from the bone surfaces of the arthroplasty target region soas to not contact the bone surfaces when the bone mating surfaces40-3904, 40-3906 and 40-3908 matingly receive and contact the bonesurfaces of the arthroplasty target region corresponding to regions3904, 3906 and 3908.

As can be understood from FIG. 39B, depending on the patient's bonetopography, the overestimation process disclosed herein may result inbone mating surfaces 40-3904, 40-3906 and 40-3908 that are actuallymultiple bone mating surfaces and/or substantially smaller than depictedin FIG. 39B. For example, the lateral condyle bone mating surface40-3906 may actually be an anterior lateral condyle bone mating surface40-3906A and a distal lateral condyle bone mating surface 40-3906D, withthe areas of the lateral condyle bone mating surface 40-3906 outside theanterior and distal bone mating surfaces 40-3906A and 40-3906D being theresult of the overestimation process so as to not contact thecorresponding bone surfaces when the anterior and distal mating surfaces40-3906A and 40-3906D matingly receive and contact their respectivecorresponding bone surfaces. The anterior and distal bone matingsurfaces 40-3906A and 40-3906D may be configured and positioned in thejig inner surface 100 to matingly receive and contact the anterior anddistal optimal target areas 3906A and 3906D discussed above with respectto FIG. 39A.

As can be understood from FIG. 39B, the medial condyle bone matingsurface 40-3908 may actually be an anterior medial condyle bone matingsurface 40-3908A and a distal medial condyle bone mating surface40-3908D, with the areas of the medial condyle bone mating surface40-3908 outside the anterior and distal mating surfaces 40-3908A and40-3908D being the result of the overestimation process so as to notcontact the corresponding bone surfaces when the anterior and distalbone mating surfaces 40-3908A and 40-3908D matingly receive and contacttheir respective corresponding bone surfaces. The anterior and distalbone mating surfaces 40-3908A and 40-3908D may be configured andpositioned in the jig inner surface 100 to matingly receive and contactthe anterior and distal optimal target areas 3908A and 3908D discussedabove with respect to FIG. 39A.

As can be understood from FIG. 39B, the anterior shaft bone matingsurface 40-3904 may actually be a smaller anterior shaft bone matingsurface 40-3904A, with the area of the anterior shaft bone matingsurface 40-3904 outside the smaller anterior mating surface 40-3904Abeing the result of the overestimation process so as to not contact thecorresponding bone surface when the smaller anterior mating surface40-3904A matingly receives and contacts its corresponding bone surface.The smaller anterior bone mating surface 40-3904A may be configured andpositioned in the jig inner surface 100 to matingly receive and contactthe anterior optimal target area 3904A discussed above with respect toFIGS. 39A and 39D.

As can be understood from FIG. 39C, which is a anterior-posteriorcross-section of the femur jig 2A of FIG. 39B mounted on the femurdistal end 3900 of FIG. 39A, the interior or bone-facing side 100 isformed of bone mating surfaces 40-3904, 40-3906 and 40-3908 andspaced-apart surfaces 100′ (i.e., bone-facing surfaces 100 that are aproduct of the overestimation process and are spaced-apart from thecorresponding bone surfaces of the arthroplasty target region 3902). Asindicated by the plurality of opposed arrows in regions 3984, 3986 and3988, the bone mating surfaces 40-3904, 40-3906 and 40-3908 matinglyreceive and contact the corresponding bone surfaces 3904, 3906 and 3908to form mating surface contact regions 3984, 3986 and 3988. Conversely,the spaced-apart surfaces 100′ are spaced apart from the correspondingbone surfaces to form spaced-apart non-contact regions 3999, wherein thespaced-apart surfaces 100′ do not contact their corresponding bonesurfaces. In addition to having the mating surfaces 40-3904, 40-3906 and40-3908 and the spaced-apart surfaces 100′, the femur jigs 2A may alsohave a saw cutting guide slot 30 and anterior and posterior drill holes32A and 32P, as discussed above.

The arrows in FIG. 39C represent a situation where the patient's bonetopography and the resulting overestimation process has generated bonemating surfaces 40-3904, 40-3906 and 40-3908 that match the targetregions 3904, 3906 and 3908, which are generally coextensive with theentirety of their respective potential regions as discussed above. Ofcourse, where the patient's bone topography and the resultingoverestimation process generates bone mating surfaces 40-3904A,40-3906A, 40-3906D, 40-3908A and 40-3908D that match the target areas3904A, 3906A, 3906D, 3908A and 3908D, which are substantially smallerthan their respective target regions 3904, 3906 and 3908, the matingsurface contact regions 3984, 3986 and 3988 may be smaller and/orsegmented as compared to what is depicted in FIG. 39C.

FIG. 40 depicts closed-loop contour lines 4002, 4004, and 4006 that areimage segmented from image slices, wherein the contour lines outline thecortical bone surface of the lower end of the femur. These contour lines4002, 4004, and 4006 may be identified via image segmentation techniquesfrom medical imaging slices generated via, e.g., MRI or CT.

As shown in FIG. 40, there are posterior portions of the contour lines(indicated as 4007) that may be of no interest during overestimationbecause the contour line region 4007 corresponds to a region of the kneethat may be inaccessible during surgery and may not correspond to a jigsurface because no part of the jig may access the region 4007 duringsurgery. An osteophyte in contour line region 4008 may be identifiedbased on the algorithm 2500. The contour lines in region 4008 may besubsequently overestimated (based on the algorithm 2500) such that theresulting jig surface does not come into contact with the osteophyte(i.e., with the osteophyte bone surface represented by contour lineregion 4008) when the jig's bone mating surface 40 matingly receives andcontacts the bone surfaces of the arthroplasty target region.Additionally, optimal contour line regions 4010 and 4012 may beidentified during execution of the algorithm 2500 as areas of thepatient's bone anatomy that have surface variations within the angularcriteria of the algorithm 2500 and, therefore, are used to generate thejig's bone mating surface 40 that matingly receives and contacts thebone surfaces of the arthroplasty target region.

Contour line region 4010 may pertain to region 3904 of FIG. 39A andfemur jig region 40-3904 of FIG. 39B. Contour line region 4012 maypertain to either region 3906 or 3908 of FIG. 39A and either femur jigregion 40-3906 or 40-3908 of FIG. 39B. Utilizing the optimal areas 4010and 4012 as jig bone mating surfaces 40 allows irregular areas of thepatient's bone anatomy to be accommodated without affecting the fit ofthe jig 2 to the patient's bone anatomy. In fact, an accurate and customfit between the jig 2 and the patient's bone anatomy can be made byusing only a few of such optimal areas. This allows substantialoverestimation of the jig surface in regions corresponding toirregularities, thereby preventing the irregularities from interferingwith an accurate and reliable fit between the jig's bone mating surfacesand those bone surfaces of the arthroplasty target region correspondingto those bone mating surfaces. The result of the overestimation processis a jig with bone mating surfaces that offer a reliable and accuratecustom fit with the arthroplasty target region. This may result in anincreased success rate for TKR or partial knee replacement surgerybecause the jig may custom fit to the most reliable bone surfaces and bedeliberately spaced from the bone surfaces that may be unreliable, forexample, because of imaging or tool machinery limitations.

2. Overestimating the 3D Tibia Surface Models

As described above with regard to block 140 of FIG. 1D, the “jig data”46 is used to produce a jigs having bone mating surfaces customized tomatingly receive the target areas 42 of the respective bones of thepatent's joint. Data for the target areas 42 may be based, at least inpart, on the 3D computer generated surface models 40 of the patient'sjoint bones. Furthermore, as described above with regard to FIG. 1A and[blocks 100-105] of FIG. 1B, these 3D computer generated surface models40 may be based on the plurality of 2D scan image slices 16 taken fromthe imaging machine 8 and, more precisely, from the contour linesderived from those 2D scan image slices via image segmentation processesknown in the art or, alternatively, as disclosed in U.S. ProvisionalPatent Application 61/126,102, which was filed Apr. 30, 2008 and isincorporated by reference herein in its entirety.

Each scan image slice 16 represents a thin slice of the desired bones.FIG. 41A illustrates the proximal axial view of the 3D model of thepatient's tibia shown in FIG. 15 with the contour lines 4101 of theimage slices shown and spaced apart by the thickness D_(T) of theslices. FIG. 41B represents a coronal view of a 3D model of thepatient's tibia with the contour lines 4101 of the image slices shownand spaced apart by the thickness D_(T) of the slices.

The slices shown in FIGS. 41A-B have contour lines 4101 similar to theopen and closed loop contour line segments 210, 210′ depicted in FIGS.2B and 2E. The contour lines 4101 of each respective image slice 16 arecompiled together to form the 3D model of the patient's tibia. Theoverall resolution or preciseness of the 3D models 40 (shown in FIG.12C) resulting from compiling together the contour lines of each ofthese slices (shown in [block 1010]) may be impacted by the thicknessD_(T) of the slices shown in FIGS. 41A-B. Specifically, the greater thethickness D_(T) of the slices, the lower the resolution/preciseness ofthe resulting 3D models, and the smaller the thickness D_(T) of theslices, the higher the resolution/preciseness of the resulting 3Dmodels.

As the resolution/preciseness of the 3D models increases, more accuratecustomized arthroplasty jigs 2 may be generated. Thus, the generalimpetus is to have thinner slices rather than thicker slices. However,depending upon the imaging technology used, the feasible thickness D_(T)of the image slices may vary and may be limited due a variety ofreasons. For example, an imaging thickness D_(T) that is sufficientlyprecise to provide the desired imaging resolution may also need to bebalanced with an imaging duration that is sufficiently brief to allow apatient to remain still for the entire imaging duration.

In embodiments utilizing MRI technology, the range of slice thicknessD_(T) may be from approximately 0.8 mm to approximately 5 mm. MRI slicethicknesses D_(T) below this range may be unfeasible because they haveassociated imaging durations that are too long for most patient's toremain still. Also, MRI slice thicknesses D_(T) below this range may beunfeasible because they may result in higher levels of noise with regardto actual signals present, residuals left between slices, and volumeaveraging limitations of the MRI machine. MRI slice thicknesses abovethis range may not provide sufficient image resolution/preciseness. Inone embodiment, the MRI slice thicknesses D_(T) is approximately 2 mm.

While embodiments utilizing CT technology may have a range of slicethicknesses D_(T) from approximately 0.3 mm to approximately 5 mm, CTimaging may not capture the cartilage present in the patient's joints togenerate the arthritic models mentioned above.

Regardless of the imaging technology used and the resultingresolution/preciseness of the 3D models, the CNC machine 10 may beincapable of producing the customized arthroplasty jigs 2 due tomechanical limitations, especially where irregularities in the bonesurface are present. This, for example, may result where a milling toolbit has dimensions that exceed those of the feature to be milled.

FIG. 42 illustrates an example sagittal view of compiled contour linesof successive sagittal 2D MRI images based on the slices shown in FIGS.41A-B with a slice thickness D_(T) of 2 mm. As can be understood fromFIGS. 41A-42, the contour lines shown begin on the medial side of theknee at the image slice corresponding to contour line 4110 and concludeon the lateral side of the knee at the image slice corresponding tocontour line 4130. Thus, in one embodiment, contour lines 4110 and 4130represent the contour lines of the first and last images slices taken ofthe tibia, with the other contour lines between contour lines 4110, 4130representing the contour lines of the intermediate image slices taken ofthe tibia. Each of the contour lines is unique is size and shape, may beeither open-loop or closed-loop, and corresponds to a unique image slice16.

FIG. 43 illustrates an example contour line 4300 of one of the contourlines depicted in FIGS. 41A-42, wherein the contour line 4300 isdepicted in a sagittal view and is associated with an image slice 16 ofthe tibia plateau. As shown, the contour line 2400 includes a pluralityof surface coordinate points (e.g., i.e., i−n, . . . , i−3, i−2, i−1, i,i+1, i+2, i+3, . . . , i+n; j−n, . . . , j−3, j−2, j−1, j, j+1, j+2,j+3, . . . , j+n; and k−n, . . . , k−3, k−2, k−1, k, k+1, k+2, k+3, . .. , k+n). The contour line and associated points may be generated byimaging technology, for example, via an image segmentation process thatmay employ, for example, a shape recognition process and/or an pixelintensity recognition process. In one embodiment, the contour line 4300may represent the boundary line along the cortical-cancellous bone edge.In one embodiment, the boundary line may represent the outer boundaryline of the cartilage surface.

Each of the surface contour points in the plurality may be separated bya distance “d”. In one embodiment, distance “d” may be a function of theminimum imaging resolution. In some embodiments, distance “d” may befunction of, or associated with, the size of the milling tool used tomanufacture the jig. For example, the distance “d” may be set to beapproximately 10 times smaller than the diameter of the milling tool. Inother words, the distance “d” may be set to be approximately 1/10^(th)or less of the diameter of the milling tool. In other embodiments, thedistance “d” may be in the range of between approximately equal to thediameter of the milling tool to approximately 1/100^(th) or less of thediameter of the milling tool.

Depending on the embodiment, the separation distance d may be eitheruniform along the contour line 4300, or may be non-uniform. For example,in some embodiments, areas of bone irregularities may have points thatare closer together than areas where no irregularities are present. Inone embodiment, the points shown along the example contour line 4300 mayhave a separation distance d of approximately 2 mm. In otherembodiments, distance d may be in the range of approximately 0.8 mm toapproximately 5 mm.

The bone surface of the example contour line 4300 includes a region4302A on the anterior portion of the tibia plateau, a region 4302B onthe tibia plateau that is representative of an irregularity, and aregion 4302C on the articular surface of the tibia plateau. Theirregularity of region 4302B may be due to a variety of patient specificfactors. For example, irregular region 4302B illustrates a type of boneirregularity, referred to as an “osteophyte”, where a bony outgrowth hasoccurred in the tibia plateau. Osteophytes may be present in patientsthat have undergone trauma to the bone or who have experienceddegenerative joint disease.

Irregularities may be due to other factors, such as cartilage damage,which may appear as notches in the contour line 4300. Regardless of thecause of the irregularities, the presence of irregularities in thecontour line 4300 may adversely impact the ability to generate a matingsurface in the actual arthroplasty jig that accurately and reliablymates with the corresponding bone surface of the patient during thearthroplasty procedure. This may be the result of the imagingimpreciseness in the vicinity of the contour irregular region 4302B orbecause the contour irregular region 4302B represents a surface contourthat is too small for the tooling of the CNC machine 10 to generate. Toaccount for contour line regions associated with imaging imprecisenessand/or features too small to be milled via the tooling of the CNCmachine, in some embodiments, such contour line regions may beidentified and corrected or adjusted via the overestimation processprior to being compiled to form the 3D models 40.

As discussed above, FIG. 25 represents an example overestimationalgorithm 2500 that may be used to identify and adjust for irregularregion 4302B when forming the 3D models 40. In block 2502, medicalimaging may be performed on the damaged bone at desired slicethicknesses D_(T), which in some embodiments may be equal to those slicethicknesses D_(T) mentioned above with regard to FIGS. 41A-B. Forexample, MRI and/or CT scans may be performed at predeterminedthicknesses D_(T) as shown in FIGS. 41A-B. In some embodiments, thedesired thickness D_(T) used in block 2502 is set at 2 mm or any otherthickness D_(T) within the range of thicknesses D_(T) mentioned above.

From this medical imaging, a series of slices 16 may be produced andimage segmentation processes can be used to generate the contour lines210, 210′, 4101, 4110, 4130, 4300 discussed with respect to FIGS. 2,41A-B, and 43 (see block 2504). Also in block 2504, a plurality ofsurface coordinate points along each contour line segment 4302A-C may beidentified as shown in FIG. 43 with respect to contour line 4300. Forexample, the points in the irregular region corresponding to contourline segment 4302B may be identified and indexed as k−n, . . . , k−3,k−2, k−1, k, k+1, k+2, k+3, . . . , k+n.

With the surface coordinate points along the contour 4300 defined, ananalysis may be performed on two or more of the points (e.g., k and k+1)to determine if an irregularity exists in the contour line segment perblock 2506.

FIG. 44 depicts implementing an example analysis scheme (according toblock 2506) on the irregular contour line region 4302B of FIG. 43. Asshown, the analysis may include constructing one or more tangent lines(labeled as t_(k−1), t_(k), t_(k+1), t_(k+2), t_(k+3), t_(k+4), etc.),corresponding to the points in the irregular region 4302B. The analysisof block 2506 may further include calculating differences between theangles formed by one or more of the tangent lines. For example, thedifference between the angles formed by the tangent lines t_(k) andt_(k+1) may be defined as w_(k), where

$w_{k} = {{\cos^{- 1}\left( \frac{t_{k + 1} \cdot t_{k}}{{t_{k + 1}}{t_{k}}} \right)}.}$In some embodiments, the operations of block 2506 may be performedrepetitively on each point within the contour segment.

The operations of block 2506 may be calculated on subsequent points(e.g., between t_(k) and t_(k+1)) in some embodiments, and onnon-subsequent points in other embodiments (e.g., t_(k+2) and t_(k+4)).

The angular difference w may indicate whether portions of the contourline segment are too eccentric for use in constructing the 3D models 40.In block 2508, the angular difference w may be compared to apredetermined angular criterion w_(c). The angular criterion w_(c) maybe determined based on several factors, including the physicaldimensions and characteristics of the CNC machine 10. In someembodiments, the predetermined angular criterion w_(c) is set atapproximately 5 degrees. In other embodiments, the predetermined angularcriterion w_(c) is set at between approximately 5 degrees andapproximately 20 degrees.

For the sake of discussing the example irregular region 4302B shown inFIG. 44, the angular criterion w_(c) is set to 5 degrees in oneembodiment. The angular differences between tangent lines associatedwith adjacent points k−4, k−3, k−2 and k+12, k+13, and k+14 are withinthe predetermined angular criterion w_(c) of 5 degrees, but thedifferences between tangent lines associated with adjacent points k−3,k−2, k−1, ki, k+1, k+2, . . . , k+10 exceeds the predetermined angularcriterion w_(c) of 5 degrees and therefore indicates an irregular regionof the contour line. As mentioned above, these irregularities may resultfrom conditions of the patient's bone such as arthritis orosteoarthritis and generally result in a contour line segment beingunsuitable for using when forming the 3D models 40. Accordingly, if thecomparison from block 2508 indicates that the angular difference w isgreater than the predetermined criterion w_(c), then the data associatedwith the irregular contour line segment may be modified byoverestimating (e.g., adjusting the irregular contour line segmentoutward or away from the bone portion of the image slice 16) asdiscussed in greater detail below with respect to FIG. 45 (see block2510).

FIG. 45 depicts the irregular region 4302B from FIG. 44 including aproposed area of overestimation 4501, wherein an overestimationprocedure creates an adjusted contour line 4502 and positionallydeviates the adjusted contour line 4502 from the original surfaceprofile contour line 4302B. In the event that the comparison performedin block 2508 indicates that the angular differences between any of thepoints k−3 through k+10 exceed the predetermined angular criterionw_(c), then the contour line segment may be overestimated between thesepoints as shown by the dashed line 4502. As can be understood from acomparison of contour line 4302B to the overestimated or adjusted line4502, the adjusted line 4502 is adjusted or moved outward or away fromthe location of the contour line 4502B by an offset distance. Dependingon the embodiment, the offset distance between the contour line 4302Band the adjusted line 4502 may range between a few millimeters to a fewcentimeters. This overestimation may be built into the data used toconstruct 3D surface models 40 and result in a gap between therespective region of the bone mating surface of the jig 2 and thecorresponding portion of the patient's bone surface, thereby avoidingcontact between these respective areas of the jig and bone surface. Theother areas, such as k−6, k−7, k−8, k−9 and k+15, k+16, k+17, and k+18,need not be overestimated, per block 2510, because the differencesbetween their tangent lines fall within the angular difference criterionw_(c). These areas may be designated as potential target areas that maylater be used as the 3D surface models 40 if other angular criteria(described below) are satisfied.

By building overestimation data into the 3D surface models 40,deliberate spaces may be created in regions of the custom arthroplastyjig 2 corresponding to irregularities in the patient's bone, where it isoften difficult to predict the size and shape of these irregularitiesfrom 2D MRI or where it is difficult to accurately machine the contourline into the jig's bone mating surface because of the largeness of themilling tool relative to the changes in contour. Thus, the jig 2 mayinclude one or more deliberate spaces to accommodate theseirregularities or inability to machine. Without these deliberate spaces,the jig 2 may be potentially misaligned during the TKR surgery and mayreduce the chances of the surgery's success.

As described above with respect to FIGS. 28 and 30, the imagegeneration, analysis and overestimation of blocks 2506, 2508 and 2510may be performed on other irregularities of contour line 4300, if suchadditional irregularities were present in FIG. 43.

As shown in FIG. 45, a tool 4504 having diameter D₂ may be employed tomachine the contour line 4302 into the jig blank. As described abovewith respect to FIG. 29A, in some embodiments, to allow for an adequatetransition from the non-overestimated regions to the overestimatedregions 4501 in view of the diameter D₂ of the tool 4504 to be used, theoverestimation may include additional points to either side of thepoints falling outside of the predetermined criterion w_(c) (i.e.,points k−3, k−4, and k−5 as well as at points k+12, k+13, and k+14).Thus, the overestimation in region 4302B may extend from k−5 throughk+14. Furthermore, since the comparison performed in block 2508indicates that the angular difference w_(k) is less than thepredetermined criterion w_(c) at points k−3, k−4, k−5, k−6, k−7, k−8,k−9 and k+12, k+13, k+14, k+15, k+16, k+17, and k+18, these points k−6,k−7, k−8, k−9 and k+15, k+16, k+17, and k+18 (adjusting for the additionof points k−3, k−4, and k−5 as well as at points k+12, k+13 to theoverestimation transition regions 4501) may be used in constructing the3D models 40 as long as other criteria (described below in the contextof blocks 2514-2520) are met.

A tool 4504 may be used to form the surface of the jig's bone matingsurface from the 3D models 40 formed from the compiled contour lines,some of which may have been modified via the overestimation process. Thetool 4504 may be part of the CNC machine 10 or any other type ofmachining or manufacturing device having any type of tool or device forforming a surface in a jig blank. Regardless of the type of the deviceused to mill or form the jigs 2, the tool 4504 may have certainattributes associated with jig machining process that are taken intoaccount when performing the overestimating per block 2510. Theassociated attributes may include the accessible space for the machiningtools to reach and machine the jig's bone mating surface. Examples ofsuch attributes may include the collar diameter of the drilling cutterdevice, the allowable angle the drilling device can make with thesurface to be drilled (e.g., 45 degrees±10%), and/or the overall lengthof the drilling cutter head.

For example, as indicated in FIG. 45, if the minimum diameter of theoverestimated region 4501 is larger than the diameter D₂ of the tool4504, then overestimation of block 2510 may not need to account for thedimensions of the tool 4504, except to provide adequate transitionsleading to the overestimated region 4501 as illustrated above by theaddition of a single or few points (e.g., points k−3, k−4, and k−5 aswell as at points k+12, k+13) to either side of the points outsidepredetermined criterion w_(c).

If, on the other hand, the tool 4504 has a diameter D₂ that is greaterthan the diameter of the overestimated region, then the overestimatedregion may be increased in diameter to account for the large tooldiameter, as described above with respect to FIGS. 29B-29C. With thecurves overestimated to account for factors related to the tool 4504,the resulting overestimated surface profile or contour may be saved forgenerating the 3D model 40 as long as other criteria (described below inthe context of block 2514-2520) are met.

FIGS. 46A-B show similar analyses of the regular regions 4302A and 4302C(from FIG. 43). As was the case with the irregular region 4302B, pointsi+2, i+3, i+n and j+1, j+2, j+3, j+n along the contour line 4300 may beidentified for regions 4302A and 4302C and then tangent lines (labeledas t_(j+1), t_(j+2), t_(j+3), etc. and t_(i+1), t_(i+2), t_(i+3), etc.)may be constructed per block 2506. Per block 2508, comparing the angulardifferences w between these tangent lines using the formulas

$w_{j} = {{\cos^{- 1}\left( \frac{t_{j + 1} \cdot t_{j}}{{t_{j + 1}}{t_{j}}} \right)}\mspace{14mu}{and}}$$w_{i} = {\cos^{- 1}\left( \frac{t_{i + 1} \cdot t_{i}}{{t_{i + 1}}{t_{i}}} \right)}$shows that they w_(j), w_(i) are within the angular criterion w_(c),which in this example is 5 degrees. Thus, the points of the regions4302A and 4302C shown in FIGS. 46A-B may be saved and used as potentialsurface profiles for the mating surface of the tibial jig if the surfacevariations between these points and points on contour lines of adjacentslices are not too extreme. That is, if the angular differencesassociated with a contour line of a particular slice fall within theangular criterion w_(c), and the points are used as a potential jigsurface, then surface variation between contour lines of adjacent slicesmay be checked in block 2514. This approach may help to identify certainareas where no cartilage damage or osteophyte is observed in theimaging, yet there is a need to overestimate because the surfacevariation, between the adjacent slices shown in FIGS. 41A-B, may be toogreat to be used as an accurate representation of the actual bonesurface to be a potential tibial jig surface. Example areas fallingwithin this category for the proximal tibia plateau include the areasnear the medial and lateral tibial plateaus adjacent to, and including,the spine portion to name a few examples.

Once it is determined that a specific portion of a contour line hassatisfied the criterion w_(c) of block 2508 of FIG. 25, that contourline portion may be further analyzed to determine if the contour lineportion also satisfies both of the criterion θ_(c) and φ_(c) of block2514, as discussed above with respect to FIGS. 25 and 32A-33B. Morespecifically, corresponding coordinate points are determined via any ofthe three methods discussed above with respect to FIGS. 33A-33F. Thesurface variation between the corresponding coordinate points isanalyzed as discussed with above with respect to FIGS. 33A-33F withrespect to: (1) angular deviation θ between corresponding coordinatepoints of contour lines of adjacent image slices; and (2) the angulardifferences φ of normal vectors associated with corresponding coordinatepoints of contour lines of adjacent image slices. If the contour lineportion meets all of the criterion w_(i), θ_(c) and φ_(c) of blocks 2508and 2514 of FIG. 25, then, as discussed above and indicated in block2520 of FIG. 25, the contour line portion may be recorded and employedin generating the jig's bone mating surfaces. Alternatively, if thecontour portion line fails to meet any one or more of the criterionw_(i), θ_(c) and φ_(c) of blocks 2508 and 2514, then as indicated inFIG. 25 and discussed above, the contour line portion may be modifiedper the overestimation process (block 2510) or, in some instances, theimage slice thickness D_(T) may be reset to a more narrow thicknessD_(T) and the entire process repeated beginning at block 2502 of FIG.25.

FIG. 47 is a proximal view of the tibia plateau similar to that of FIG.15 depicting contour lines 4700 produced by imaging the left tibia at animage spacing D_(T) of, for example, 2 mm. As shown, the contour lines4700 may be grouped into multiple regions in the lateral-medialdirection 4702-4708 for the sake of discussion. The region 4702 includesthe contour lines 4700 of the most medial half of the medial tibialplateau and extends laterally from the most medial side of the medialtibial plateau to the medial-lateral middle of the medial tibialplateau. The region 4704 includes the contour lines 4700 of the mostlateral half of the medial tibial plateau and extends laterally from themiddle of the medial tibial plateau to the medial-lateral point near thetibial spine. The region 4706 includes the contour lines 4700 of themost medial half of the lateral tibial plateau and extends laterallyfrom the medial-lateral point near the tibial spine to themedial-lateral middle of the lateral tibial plateau. The region 4708includes the contour lines 4700 of the most lateral half of the lateraltibial plateau and extends laterally from the medial-lateral middle ofthe lateral tibial plateau to the most lateral side of the lateraltibial plateau.

FIG. 48 is a sagittal view of the contour lines 4700 of region 4702 ofFIG. 47. The contour lines 4700 of region 4702 include contour lines4802-4812, with the most medial portion of the medial tibial plateaubeing indicated by contour line 4802. The size of each successivecontour line 4700 of region 4702 increases moving laterally from themost medial contour line 4802 of region 4702 to the most lateral contourline 4812 of region 4702, which is near the medial-lateral middle of themedial tibial plateau.

As can be understood from FIG. 48, the contour lines 4802-4803 arespaced apart from their respective adjacent contour lines a substantialamount around their entire boarders. Such wide spacing corresponds to asubstantial amount of rise or fall distances between adjacent contourlines, as discussed above with respect to FIG. 33B. Thus, such contourlines would likely fail to meet the angular criterion θ_(c) and besubject to the overestimation process such that jig surfacescorresponding to the contour lines 4802-4803 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 48, in the proximal portion of the medialtibial plateau, the contour lines 4804-4812 in the region 4814 convergesuch that there is little, if any, amount of rise or fall distancebetween adjacent contour lines. Thus, such contour lines 4804-4812 inthe region 4814 would likely meet the first angular criterion θ_(c).Similarly, in the anterior tibial plateau portion of the proximal tibia,the contour lines 4811-4812 in region 4816 converge such that there islittle, if any, amount of rise or fall distance between adjacent contourlines. Thus, such contour lines 4804-4812 in region 4814 and contourlines 4811-4812 in region 4816 would likely meet the first angularcriterion θ_(c).

As can be understood from the arrows in regions 4814 and 4816, theangular differences between normal vectors for the contour line portionswithin regions 4814 and 4816 would be minimal, likely meeting the secondangular criterion φ_(c). Thus, as the portions of the contour lines4804-4812 within region 4814 and the portions of the contour lines4811-4812 within region 4816 likely meet both angular criterion θ_(c)and φ_(c), the portions of the contour lines 4804-4812 within the region4814 and the portions of the contour lines 4811-4812 within region 4816represent optimal contact areas 4814 and 4816 for mating contact withthe jig's bone mating surface 40.

In one embodiment, as can be understood from FIG. 52A discussed below,the optimal contact area 4814 may be the surface of the medial tibialplateau that displaces against the corresponding articular surface ofthe medial femoral condyle, and the optimal contact area 4816 may be themedial anterior region of the proximal tibia just distal of the tibialplateau edge and medial of the tuberosity of the tibia.

In one embodiment, the optimal contact areas 4814 and 4816 matinglycorresponds to the jig's bone mating surface 40 such that the portionsof the contour lines 4702 indicated by regions 4814 and 4816 may be usedto generate the jig's bone mating surface 40, per the algorithm 2500 ofFIG. 25. Conversely, per the algorithm 2500, the portions of the contourlines 4702 outside regions 4814 and 4816 may be subjected to theoverestimation process discussed above such that the jig's surfacescreated from the overestimated contour line portions results in jigsurfaces that do not contact the corresponding portions of the patient'sarthroplasty target regions.

FIG. 49 is a sagittal view of the contour lines 4700 of region 4704 ofFIG. 47. The contour lines 4700 of region 4704 include contour lines4902, 4903, 4904, 4905, 4906, 4907, 4908, 4909 and 4910 with the mostmedial portion of region 4704 being indicated by contour line 4802,which is near the medial-lateral middle of the medial tibial plateau,and the most lateral portion of region 4704 being indicated by contourline 4810, which is a medial-lateral point near the tibial spine. Thesize of each successive contour line 4700 of region 4704 increasesmoving laterally from the most medial contour line 4902 to the mostlateral contour line 4910.

As can be understood from FIG. 49, the contour lines 4902-4910 arespaced apart from their respective adjacent contour lines a substantialamount in their posterior and anterior portions along the shaft of thetibia, and to a lesser extent in their tibia spine portions. Such widespacing corresponds to a substantial amount of rise or fall distancesbetween adjacent contour lines, as discussed above with respect to FIG.33B. Thus, such contour lines would likely fail to meet the angularcriterion θ_(c) and be subject to the overestimation process such thatjig surfaces corresponding to the contour lines 4902-4910 would notcontact the corresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 49, in the anterior tibial plateauportion of the proximal tibia, the contour lines 4902-4910 in the region4912 converge such that there is little, if any, amount of rise or falldistance between adjacent contour lines. Thus, such contour lines4902-4910 in the region 4912 would likely meet the first angularcriterion θ_(c).

As can be understood from the arrows in region 4912, the angulardifferences between normal vectors for the contour line portions withinthe region 4912 would be minimal, likely meeting the second angularcriterion φ_(c). Thus, as the portions of the contour lines 4902-4910within region 4912 likely meet both angular criterion θ_(c) and φ_(c),the portions of the contour lines 4902-4910 within the region 4912represent an optimal contact area 4912 for mating contact with the jig'sbone mating surface 40.

In one embodiment, the optimal contact area 4912 matingly corresponds tothe jig's bone mating surface 40 such that the portions of the contourlines 4902-4910 indicated by region 4912 may be used to generate thejig's bone mating surface 40, per the algorithm 2500 of FIG. 25.Conversely, per the algorithm 2500, the portions of the contour lines4902-4910 outside region 4912 may be subjected to the overestimationprocess discussed above such that the jig's surfaces created from theoverestimated contour line portions results in jig surfaces that do notcontact the corresponding portions of the patient's arthroplasty targetregions.

In one embodiment, as can be understood from FIG. 52A discussed below,the optimal contact area 4912 may be the anterior region of the proximaltibia just distal of the tibial plateau edge and just distal of thetuberosity of the tibia, extending medial-lateral from just medial ofthe tuberosity of the tibia to generally centered medial-lateralrelative to the tuberosity of the tibia.

FIG. 50 is a sagittal view of the contour lines 4700 of region 4706 ofFIG. 47. The contour lines 4700 of region 4706 include contour lines5002, 5003, 5004, 5005, 5006, 5007, 5008, 5009 and 5010 with the mostmedial portion of region 4706 being indicated by contour line 5002,which is a medial-lateral point near the tibial spine, and the mostlateral portion of region 4704 being indicated by contour line 5010,which is near the medial-lateral middle of the lateral tibial plateau.The size of each successive contour line 4700 of region 4704 decreasesmoving laterally from the most medial contour line 5002 to the mostlateral contour line 5010.

As can be understood from FIG. 50, the contour lines 5002-5010 arespaced apart from their respective adjacent contour lines a substantialamount in their posterior and anterior portions along the shaft of thetibia, and to a lesser extent in their tibia spine and tibia tuberosityportions. Such wide spacing corresponds to a substantial amount of riseor fall distances between adjacent contour lines, as discussed abovewith respect to FIG. 33B. Thus, such contour lines would likely fail tomeet the angular criterion θ_(c) and be subject to the overestimationprocess such that jig surfaces corresponding to the contour lines5002-5010 would not contact the corresponding surfaces of thearthroplasty target areas.

As can be understood from FIG. 50, in the anterior tibial plateauportion of the proximal tibia, the contour lines 5002-5010 in the region5012 converge such that there is little, if any, amount of rise or falldistance between adjacent contour lines. Thus, such contour lines5002-5010 in the region 5012 would likely meet the first angularcriterion θ_(c).

As can be understood from the arrows in region 5012, the angulardifferences between normal vectors for the contour line portions withinthe region 5012 would be minimal, likely meeting the second angularcriterion φ_(c). Thus, as the portions of the contour lines 5002-5010within region 5012 likely meet both angular criterion θ_(c) and φ_(c),the portions of the contour lines 5002-5010 within the region 5012represent an optimal contact area 5012 for mating contact with the jig'sbone mating surface 40.

In one embodiment, the optimal contact area 5012 matingly corresponds tothe jig's bone mating surface 40 such that the portions of the contourlines 5002-5010 indicated by region 5012 may be used to generate thejig's bone mating surface 40, per the algorithm 2500 of FIG. 25.Conversely, per the algorithm 2500, the portions of the contour lines5002-5010 outside region 5012 may be subjected to the overestimationprocess discussed above such that the jig's surfaces created from theoverestimated contour line portions results in jig surfaces that do notcontact the corresponding portions of the patient's arthroplasty targetregions.

In one embodiment, as can be understood from FIG. 52A discussed below,the optimal contact area 5012 may be the anterior region of the proximaltibia just distal of the tibial plateau edge and just distal of thetuberosity of the tibia, extending medial-lateral from just lateral ofthe tuberosity of the tibia to generally centered medial-lateralrelative to the tuberosity of the tibia.

FIG. 51 is a sagittal view of the contour lines 4700 of region 4708 ofFIG. 47. The contour lines 4700 of region 4708 include contour lines5102-5112, with the most lateral portion of the lateral tibial plateaubeing indicated by contour line 5102. The size of each successivecontour line 4700 of region 4708 increases moving laterally from themost medial contour line 5102 of region 4708, which is near themedial-lateral middle of the medial tibial plateau, to the most lateralcontour line 5110 of region 4708, which is the most lateral portion ofthe lateral tibial plateau.

As can be understood from FIG. 51, the contour lines 5110-5112 arespaced apart from their respective adjacent contour lines a substantialamount around their entire boarders. Such wide spacing corresponds to asubstantial amount of rise or fall distances between adjacent contourlines, as discussed above with respect to FIG. 33B. Thus, such contourlines would likely fail to meet the angular criterion θ_(c) and besubject to the overestimation process such that jig surfacescorresponding to the contour lines 5110-5112 would not contact thecorresponding surfaces of the arthroplasty target areas.

As can be understood from FIG. 51, in the proximal portion of thelateral tibial plateau, the contour lines 5102-5109 in the region 5114converge such that there is little, if any, amount of rise or falldistance between adjacent contour lines. Thus, such contour lines5102-5109 in the region 5114 would likely meet the first angularcriterion θ_(c). Similarly, in the anterior tibial plateau portion ofthe proximal tibia, the contour lines 5102-5105 in region 5116 convergesuch that there is little, if any, amount of rise or fall distancebetween adjacent contour lines. Thus, such contour lines 5102-5109 inregion 5114 and contour lines 5102-5105 in region 5116 would likely meetthe first angular criterion θ_(c).

As can be understood from the arrows in regions 5114 and 5116, theangular differences between normal vectors for the contour line portionswithin regions 5114 and 5116 would be minimal, likely meeting the secondangular criterion φ_(c). Thus, as the portions of the contour lines5102-5109 within region 5114 and the portions of the contour lines5102-5105 within region 4816 likely meet both angular criterion θ_(c)and φ_(c), the portions of the contour lines 5102-5109 within the region5114 and the portions of the contour lines 5102-5105 within region 5116represent optimal contact areas 5114 and 5116 for mating contact withthe jig's bone mating surface 40.

In one embodiment, as can be understood from FIG. 52A discussed below,the optimal contact area 5114 may be the surface of the lateral tibialplateau that displaces against the corresponding articular surface ofthe lateral femoral condyle, and the optimal contact area 5116 may bethe lateral anterior region of the proximal tibia just distal of thetibial plateau edge and lateral of the tuberosity of the tibia.

In one embodiment, the optimal contact areas 5114 and 5116 matinglycorresponds to the jig's bone mating surface 40 such that the portionsof the contour lines 4708 indicated by regions 5114 and 5116 may be usedto generate the jig's bone mating surface 40, per the algorithm 2500 ofFIG. 25. Conversely, per the algorithm 2500, the portions of the contourlines 4708 outside regions 5114 and 5116 may be subjected to theoverestimation process discussed above such that the jig's surfacescreated from the overestimated contour line portions results in jigsurfaces that do not contact the corresponding portions of the patient'sarthroplasty target regions.

As can be understood from the preceding discussion, the overestimationprocess disclosed herein can be used to identifying optimal target areas(e.g., optimal target areas 4814, 4816, 4912, 5012, 5114, 5116 asdiscussed with respect to FIGS. 47-51). More specifically, theoverestimation process disclosed herein can employ these optimal targetareas to generate the bone mating surfaces 40 of the jigs 2 whilecausing the other surface areas of the jigs to be configured such thatthese other jig surface areas will not contact the surfaces of thearthroplasty target areas when the jig's bone mating surfaces 40 havematingly received and contacted the arthroplasty target areas. Theresult is a jig that has bone mating surfaces 40 that are based on theregions of the arthroplasty target region that are most accuratelyrepresented via 3D computer modeling and most likely to be machinableinto the jig. Such a jig provides an increased accuracy of fit betweenthe jig's mating surface 40 and the arthroplasty target areas of thepatient's bone.

For most patients, it is common that the overestimation process outlinedin FIG. 25 will result in certain areas of the tibial arthroplastytarget region being identified as the optimal target areas discussedabove with respect to FIGS. 47-51. For example, as depicted in FIG. 52A,which is proximal-sagittal isometric view of a tibial proximal end 5200,a commonly encountered, healthy, non-deformed tibial proximal end 5200may have an arthroplasty target region 5202 with certain optimal targetregions 5204, 5206 and 5208. These optimal target regions 5204, 5206 and5208 commonly identified on most patients via the overestimation processof FIG. 25 are indicated in FIG. 52A by the cross-hatched regions. Ithas been found that these optimal target regions 5204, 5206 and 5208 arethe regions of the arthroplasty target region 5202 that are most likelyto satisfy the criterion w_(i), θ_(c) and φ_(c) of blocks 2508 and 2514of FIG. 25. Therefore, these target regions 5204, 5206 and 5208 may beused to generate the jig's bone mating surfaces 40.

While, in one embodiment, the overestimation process of FIG. 25 islikely to result in optimal target regions such as those indicated viathe cross-hatching regions 5204, 5206 and 5208, in other embodiments,the optimal target regions may result in target regions in otherlocations on the tibial proximal end 5200 that are in addition to, or inplace of, those regions 5204, 5206 and 5208 depicted in FIG. 52A.

One of the benefits of the overestimation process of FIG. 25 is that itidentifies two types of contour lines 210, the first type being thosecontour lines that are most likely to be unacceptable for the generationa jig's bone mating surfaces 40, and the second type being those contourlines that are most likely to be acceptable for the generation of ajig's bone mating surfaces 40. The first type of contour lines areunlikely to be acceptable for the generation of a jig's bone matingsurfaces 40 because they pertain to bone surfaces that are too varied tobe accurately 3D computer modeled and/or are such that they are notreadily machinable into the jig blank. Conversely, the second type ofcontour lines are likely to be acceptable for the generation of a jig'sbone mating surfaces 40 because they pertain to bone surfaces that varysuch an insubstantial amount that they can be accurately 3D computermodeled and are such that they are readily machinable into the jigblank. While optimal target regions 5204, 5206 and 5208 representregions likely corresponding to contour lines of the second type formost commonly encountered patients, the overestimation processesdisclosed herein may be adapted to result in other or additional optimaltarget regions.

In some instances the entirety of the target regions 5204, 5206 and 5208may correspond to the second type of contour lines, namely those type ofcontour lines that satisfy the criterion w_(i), θ_(c) and φ_(c) ofblocks 2508 and 2514 of FIG. 25. In such instances, the entirety of thetarget regions 5204, 5206 and 5208 are matingly contacted by the jig'sbone mating surface 40.

However, in some instances one or more potions of one or more of thetarget regions 5204, 5206 and 5208 may be subjected to overestimation sothat the jig's bone mating surface 40 does not contact such portions ofthe target regions 5204, 5206 and 5208, although the jig's bone matingsurface 40 still matingly contacts the other portions of the targetregions 5204, 5206 and 5208 corresponding to the second type of contourlines. Such a situation may arise, for example, where a substantialsurface variation (e.g., a hole, deformity or osteophyte) exists on atibial plateau articular surface 5218, 5219 that meets the criterionw_(i), θ_(c) and φ_(c) of blocks 2508 and 2514 for the rest of itssurface.

The overestimation process disclosed herein may result in theidentification of target regions 5204, 5206 and 5208 that are mostlikely to result in bone mating surfaces 40 of jigs 2 that are readilymachinable into the jigs 2 and most likely to facilitate reliable andaccurate mating of the jigs to the arthroplasty target regions. Theoverestimation process results in such accurate and reliable bone matingsurfaces 40 while causing other surfaces of the jigs 2 corresponding toless predictable bone surfaces to not contact the bone surfaces when thebone mating surfaces 40 matingly receive the target regions 5204, 5206and 5208 of the actual arthroplasty target region.

As indicated in FIG. 52A by the cross-hatched regions, optimal targetregions 5204, 5206 and 5208 may include three general areas of thetibial plateau 5210. For example, the anterior optimal target region5204 may include the anterior portion of the tibial proximal end 5200just distal of the anterior edge 5212 of the tibia plateau 5210 and justproximal of the tibial tuberosity 5214, the anterior optimal targetregion 5204 extending both medial and lateral of the tuberosity. Also,for example, the medial optimal target region 5206 may include thearticular portion of the medial tibial plateau 5220 (i.e., the portionof the medial tibial plateau 5224 that articulates against thearticulate surface of the medial femoral condyle), and the lateraloptimal target region 5208 may include the articular portion of thelateral tibial plateau 5222 (i.e., the portion of the lateral tibialplateau 5226 that articulates against the articulate surface of thelateral femoral condyle).

As indicated in FIG. 52A, the tibial proximal end 5200 may include amedial tibial plateau 5224, a lateral tibial plateau 5226, a tibialspine 5228 separating the two plateaus 5224, 5226, a tibial tuberosity5214, and a tibial shaft 5230 extending distally from the tibial plateauregion 5210. Each plateau 5224 and 5226 includes an articular surface5220 and 5222 that articulates against corresponding articular surfacesof the femoral condyles.

As indicated in FIG. 52E, which is a coronal view of the anterior sideof the tibial proximal end 5200, the medial tibial plateau 5224 andlateral tibial plateau 5226 converge to form the tibial spine 5228,which separates the two plateaus 5224, 5226 and forms the intercondyloideminence 52E1. The tibial shaft 5230 distally extends from the tibialplateau region 5210, and the tibial tuberosity 5214 is located on aproximal region of the shaft 5230. The lateral meniscus is indicated at52E2, the capsule is indicated at the dashed line at 52E3, the lateralcondyle is located at 52E4, the biceps and the anterior tibio-fibularligament are indicated at 52E5, the fibular lateral ligament isindicated at 52E6, the lateral digitorum longus is indicated at 52E7,the lateral surface of the tibia shaft or tibialis anterior is indicatedat 52E17, the semitendinosus is indicated at 52E8, the sartorius isindicated at 52E9, the graoilis is indicated at 52E10, the distalportion of the ligamentum patella is indicated at 52E11, the tibiallateral ligament is indicated at 52E12, the medial condyle is indicatedat 52E13, the anterior crucial ligament is indicated at 52E14, thecoronary ligament is indicated at 52E15, and the medial meniscus isindicated at 52E16.

As indicated in FIG. 52A by the cross-hatching, in one embodiment, themedial optimal target region 5206 may be generally coextensive with themedial articular surface 5220 that articulates against the respectivearticulate surface of the medial femoral condyle. In one embodiment, themedial optimal target region 5220 may extend: anterior-posterior betweenthe anterior edge 5240 and posterior edge 5242 of the medial tibialplateau 5224; and lateral-medial between the medial side 5446 of themedial tibial plateau 5224 and the medial base 5248 of the medial tibialspine. In one embodiment as can be understood from FIG. 52A, the medialoptimal target region 5206 may be the entire cross-hatched region 5206or any one or more portions of the cross-hatched region 5206.

In one embodiment as indicated in FIG. 52A by the double cross-hatching,a medial target area 5206A may be identified within the medial optimaltarget region 5206 via the overestimation process disclosed herein.Thus, although the medial optimal target region 5206 may be generallycoextensive with the medial articular surface 5220, the actual areawithin the medial optimal target region 5206 identified as being areliable surface for the generation of the mating surfaces ofarthroplasty jigs may be limited to a medial target area 5206A, theremainder of the medial optimal target region 5206 being subjected tothe overestimation process. The medial target area 5206A may be locatednear a central portion of the optimal target region 5206.

As indicated in FIG. 52A by the cross-hatching, in one embodiment, thelateral optimal target region 5208 may be generally coextensive with thelateral articular surface 5222 that articulates against the respectivearticulate surface of the lateral femoral condyle. In one embodiment,the lateral optimal target region 5222 may extend: anterior-posteriorbetween the anterior edge 5250 and posterior edge 5252 of the lateraltibial plateau 5226; and lateral-medial between the lateral side 5256 ofthe lateral tibial plateau 5226 and the lateral base 5258 of the lateraltibial spine. In one embodiment as can be understood from FIG. 52A, thelateral optimal target region 5208 may be the entire cross-hatchedregion 5208 or any one or more portions of the cross-hatched region5208.

In one embodiment as indicated in FIG. 52A by the double cross-hatching,a lateral target area 5208A may be identified within the lateral optimaltarget region 5208 via the overestimation process disclosed herein.Thus, although the lateral optimal target region 5208 may be generallycoextensive with the lateral articular surface 5222, the actual areawithin the lateral optimal target region 5208 identified as being areliable surface for the generation of the mating surfaces ofarthroplasty jigs may be limited to a lateral target area 5208A, theremainder of the lateral optimal target region 5208 being subjected tothe overestimation process. The lateral target area 5208A may be locatednear a central portion of the optimal target region 5208.

As indicated in FIG. 52A by the cross-hatching, in one embodiment, theanterior optimal target region 5204 may be an anterior surface of thetibia plateau region 5202 distal of the joint line or, morespecifically, distal of the anterior tibia plateau edge 5212. Theanterior optimal target region 5204 may be the anterior region of theproximal end of the tibia extending between the plateau edge 5212 andthe proximal edge 5255 of the tibia tuberosity 5214. The anterior targetregion 5204 may extend distally along the tibia adjacent to the medialand lateral edges 5256, 5257 of the tibia tuberosity 5214. The anteriortarget region 5204 may extend medially to the anterior medial edge 5260of the tibia, and laterally to the anterior lateral edge 5261 of thetibia.

As shown in FIG. 52E by the cross-hatching, the anterior optimal targetregion 5204 may be divided into three sub-regions 5204-1, 5204-2 and5204-3. The first or medial sub-region 5204-1 may be a generally planarsurface region that extends distally from generally the plateau edge5212 or capsule line 52E3 to a point generally even with the beginningof the distal half to distal third of the tibial tuberosity 5214. Themedial sub-region 5204-1 may extend medial-lateral from the medial edgeof the medial tibia condyle to a point generally even with a medial edgeof the tibial tuberosity 5214. The medial sub-region 5204-1 maygenerally taper is the distal direction to be generally triangular.

The second or middle sub-region 5204-2 may be a generally planar surfaceregion that extends distally from generally the plateau edge 5212 orcapsule line 52E3 to a point near the proximal boundary of the tibialtuberosity 5214. The middle sub-region 5204-2 may extend medial-lateralfrom the lateral edge of the medial sub-region 5204-1 to a pointgenerally even with a lateral edge of the tibial tuberosity 5214. Thefirst sub-region 5204-1 may be generally rectangular, with the longlength extending medial-lateral.

The third or lateral sub-region 5204-3 may be a generally planar surfaceregion that extends distally from generally the plateau edge 5212 orcapsule line 52E3 to a point generally even with the beginning of thedistal two-thirds to distal three-quarters of the tibial tuberosity5214. The lateral sub-region 5204-3 may extend medial-lateral from thelateral edge of the middle sub-region 5204-2 to a lateral edge of thelateral tibia condyle. The lateral sub-region 5204-3 may generally taperis the distal direction to be generally triangular.

In one embodiment as can be understood from FIGS. 52A and 52E, theanterior target region 5204 may be the entire cross-hatched region 5204or any one or more sub-regions 5204-1, 5204-2, 5204-3 of thecross-hatched region 5204 or any one or more portions of the sub-regions5204-1, 5204-2, 5204-3. For example, as indicated by the doublecross-hatching, each sub-region 5204-1, 5204-2 and 5204-3 may have arespective target area 5204-1A, 5204-2A and 5204-3A therein that may beidentified via the overestimation process disclosed herein. Thus,although the anterior optimal target region 5204, or more specifically,its sub-regions 5204-1, 5204-2, 5204-3 may be generally coextensive withthe three generally planar surface areas identified above with respectto FIG. 52E, the actual areas within the anterior optimal target region5204 identified as being a reliable surface for the generation of themating surfaces of arthroplasty jigs may be limited to an target areas5204-1A, 5204-2A and 5204-3A, the remainder of the sub-regions 5204-1,5204-2, 5204-3 being subjected to the overestimation process. Theanterior target areas 5204-1A, 5204-2A and 5204-3A may be located anywhere within the respective sub-regions 5204-1, 5204-2, 5204-3.

FIGS. 52B-C and are, respectively, top and bottom perspective views ofan example customized arthroplasty tibial jig 2B that has been generatedvia the overestimation process disclosed herein. Similar to the femoraljig 2A depicted in FIGS. 1H and 1I, the tibia jig 2B of FIGS. 52B-Cincludes an interior or bone-facing side 104 and an exterior side 106.When the jig 2B is mounted on the arthroplasty target region during asurgical procedure, the bone-facing side 104 faces the surface of thearthroplasty target region while the exterior side 106 faces in theopposite direction.

The interior or bone-facing side 104 of the tibia cutting jig 2Bincludes bone mating surfaces 40-5204, 40-5206 and 40-5208 that: aremachined into the jig interior or bone-facing side 104 based on contourlines that met the criterion of blocks 2508 and 2514 of FIG. 25; andrespectively correspond to the optimal target regions 5204, 5206 and5208 of FIG. 52A. The rest 104′ of the interior or bone-facing side 104(i.e., the regions 104′ of the interior or bone facing sides 104 outsidethe bounds of bone mating surfaces 40-5204, 40-5206 and 40-5208) are theresult of the overestimation process wherein the corresponding contourlines failed to meet one or more of the criterion of blocks 2508 and2514 of FIG. 25 and, consequently, were moved away from the bonesurface. As a result, the interior side surface 104′ is machined to bespaced away from the bone surfaces of the arthroplasty target region soas to not contact the bone surfaces when the bone mating surfaces40-5204, 40-5206 and 40-5208 matingly receive and contact the bonesurfaces of the arthroplasty target region corresponding to regions5204, 5206 and 5208.

As can be understood from FIG. 52C, the medial bone mating surface40-5206 may include a smaller sub region bone mating surface 40-5206A,with the area of the medial bone mating surface 40-5206 outside thesmaller sub region mating surface 40-5206A being the result of theoverestimation process so as to not contact the corresponding bonesurface when the smaller sub region mating surface 40-5206A matinglyreceives and contacts its corresponding bone surface. The smaller subregion bone mating surface 40-5206A may be configured and positioned inthe jig inner surface 100 to matingly receive and contact the optimaltarget area 5206A discussed above with respect to FIGS. 52A and 52E.

As can be understood from FIG. 52C, the lateral bone mating surface40-5208 may include a smaller sub region bone mating surface 40-5208A,with the area of the lateral bone mating surface 40-5208 outside thesmaller sub region mating surface 40-5208A being the result of theoverestimation process so as to not contact the corresponding bonesurface when the smaller sub region mating surface 40-5208A matinglyreceives and contacts its corresponding bone surface. The smaller subregion bone mating surface 40-5208A may be configured and positioned inthe jig inner surface 100 to matingly receive and contact the optimaltarget area 5208A discussed above with respect to FIGS. 52A and 52E.

As can be understood from FIG. 52C, depending on the patient's bonetopography, the overestimation process disclosed herein may result in ananterior bone mating surface 40-5204 that is actually multiple bonemating surfaces have sub region mating surfaces that may besubstantially smaller than surface 5204 depicted in FIGS. 52A and 52E.For example, the anterior bone mating surface 40-5204 may actually bemade of an anterior medial bone mating surface 40-5204-1, an anteriormiddle bone mating surface 40-5204-2 and an anterior lateral bone matingsurface 40-5204-3. These mating surfaces 40-5204-1, 40-5204-2, 40-5204-3may have respective sub region bone mating surfaces 40-5204-1A,40-5204-2A, 40-5204-3A, with the areas of the mating surfaces 40-5204-1,40-5204-2, 40-5204-3 outside the respective sub region bone matingsurfaces 40-5204-1A, 40-5204-2A, 40-5204-3A being the result of theoverestimation process so as to not contact the corresponding bonesurfaces when the respective sub region bone mating surfaces 40-5204-1A,40-5204-2A, 40-5204-3A matingly receive and contact their respectivecorresponding bone surfaces. The sub region bone mating surfaces40-5204-1A, 40-5204-2A, 40-5204-3A may be configured and positioned inthe jig inner surface 100 to matingly receive and contact the respectiveoptimal target areas 5204-1A, 5204-2A, 5204-3A discussed above withrespect to FIGS. 52A and 52E.

As can be understood from FIG. 52D, which is a anterior-posteriorcross-section of the tibia jig 2B of FIGS. 52B-C mounted on the tibialproximal end 5200 of FIG. 52A, the interior or bone-facing side 104 isformed of bone mating surfaces 40-5204, 40-5206 and 40-5208 andspaced-apart surfaces 104′ (i.e., bone-facing surfaces 104 that are aproduct of the overestimation process and are spaced-apart from thecorresponding bone surfaces of the arthroplasty target region 5202). Asindicated by the plurality of opposed arrows in regions 5284, 5286 and5288, the bone mating surfaces 40-5204, 40-5206 and 40-5208 matinglyreceive and contact the corresponding bone surfaces 5204, 5206 and 5208to form mating surface contact regions 5284, 5286 and 5288. Conversely,the spaced-apart surfaces 104′ are spaced apart from the correspondingbone surfaces to form spaced-apart non-contact regions 5299, wherein thespaced-apart surfaces 104′ do not contact their corresponding bonesurfaces. In addition to having the mating surfaces 40-5204, 40-5206 and40-5208 and the spaced-apart surfaces 104′, the tibia jigs 2B may alsohave a saw cutting guide slot 30 and anterior and posterior drill holes32A and 32P, as discussed above.

The arrows in FIG. 52D represent a situation where the patient's bonetopography and the resulting overestimation process has generated bonemating surfaces 40-5204, 40-5206 and 40-5208 that match the targetregions 5204, 5206 and 5208, which are generally coextensive with theentirety of their respective potential regions as discussed above. Ofcourse, where the patient's bone topography and the resultingoverestimation process generates bone mating surfaces 40-5204-1A,40-5204-2A, 40-5204-3A, 40-5206A and 40-5208A that match the targetareas 5204-1A, 5204-2A, 5204-3A, 5206A and 5208A, which may besubstantially smaller than their respective target regions 5204-1,5204-2, 5204-3, 5206 and 5208, the mating surface contact regions 5284,5286 and 5288 may be smaller and/or segmented as compared to what isdepicted in FIG. 52D.

FIG. 53 depicts closed-loop contour lines 5302, 5304, and 5306 that areimage segmented from image slices, wherein the contour lines outline thecortical bone surface of the upper end of the tibia. These contour lines5302, 5304, and 5306 may be identified via image segmentation techniquesfrom medical imaging slices generated via, e.g., MRI or CT.

As shown in FIG. 53, there are posterior portions of the contour lines(indicated as 5307) that may be of no interest during overestimationbecause the contour line region 5307 corresponds to a region of the kneethat may be inaccessible during surgery and may not correspond to a jigsurface because no part of the jig may access the region 5307 duringsurgery. There are also portions of the contour lines (indicated as5309) which may correspond generally to the plateau edge 5212 and maynot correspond to a jig surface because no part of the jig may abutagainst or matingly engage this contour line region 5309. An osteophytein contour line region 5308 may be identified based on the algorithm2500. The contour lines in region 5308 may be subsequently overestimated(based on the algorithm 2500) such that the resulting jig surface doesnot come into contact with the osteophyte (i.e., with the osteophytebone surface represented by contour line region 5308) when the jig'sbone mating surface 40 matingly receives and contacts the bone surfacesof the arthroplasty target region. Additionally, optimal contour lineregions 5310 and 5312 may be identified during execution of thealgorithm 2500 as areas of the patient's bone anatomy that have surfacevariations within the angular criteria of the algorithm 2500 and,therefore, are used to generate the jig's bone mating surface 40 thatmatingly receives and contacts the bone surfaces of the arthroplastytarget region.

Contour line region 5310 may pertain to region 5204 of FIG. 52A andtibia jig region 40-5204 of FIG. 52B. Contour line region 5312 maypertain to either region 5206 or 5208 of FIG. 52A and either tibia jigregion 40-5206 or 40-5208 of FIG. 52C.

Utilizing the optimal areas 4310 and 4312 as jig bone mating surfaces 40allows irregular areas of the patient's bone anatomy to be accommodatedwithout affecting the fit of the jig 2 to the patient's bone anatomy. Infact, an accurate and custom fit between the jig 2 and the patient'sbone anatomy can be made by using only a few of such optimal areas. Thisallows substantial overestimation of the jig surface in regionscorresponding to irregularities, thereby preventing the irregularitiesfrom interfering with an accurate and reliable fit between the jig'sbone mating surfaces and those bone surfaces of the arthroplasty targetregion corresponding to those bone mating surfaces. The result of theoverestimation process is a jig with bone mating surfaces that offer areliable and accurate custom fit with the arthroplasty target region.This may result in an increased success rate for TKR or partial kneereplacement surgery because the jig may custom fit to the most reliablebone surfaces and be deliberately spaced from the bone surfaces that maybe unreliable, for example, because of imaging or tool machinerylimitations.

As can be understood from FIGS. 54 and 55, which are respectivelyanterior isometric views of the femur 3900 and tibia 5200, a patient'sbones 3900, 5200 may have regions that are more likely to be accuratelycomputer modeled from two dimensional medical image slices than otherregions of the patient's bones. Examples of such regions 3904, 3906,3908, 5204-1, 5204-2, 5204-3, 5206, and 5208 and how to determine suchregions are provided in the preceding discussion and also indicated inFIGS. 54 and 55.

With respect to the articular regions 3906, 3908, 5206 and 5208 of thefemur 3900 and tibia 5200, in one embodiment, where the analysis ofblocks 2508 and 2514 of FIG. 25 indicate that there is little, if anycontour line variation along a specific contour line or between adjacentcontour lines, these regions 3906, 3908, 5206 and 5208 of the femur 3900and tibia 5200 may be understood to most closely approximatecircumferential surfaces 5400, 5500 of cylinders 5402, 5504 each havingan axis 5406, 5408, 5506, 5508 extending medial-lateral and having theirrespective circumferential surfaces 5400, 5500 superimposed onto thearticular regions 3906, 3908, 5206, 5208. Accordingly, such regions3906, 3908, 5206, 5208 may be likely to be readily accurately computermodeled.

In one embodiment, the circumferential surfaces 5400, 5500 may becorrespond to an elliptical cylinder having an elliptical cross sectiontransverse to its axis 5406, 5408, 5506, 5508 and having its ellipticalmajor axis extending generally anterior-posterior and is ellipticalminor axis extending generally proximal-distal. In one embodiment, thecircumferential surfaces 5400, 5500 may be correspond to an circularcylinder having an circular cross section transverse to its axis 5406,5408, 5506, 5508.

It should be noted that the overestimation process discussed above withrespect to FIGS. 22A-55 is useful for the generation of customizedarthroplasty jigs, regardless of whether the arthroplasty jigs areconfigured to produce natural alignment or zero degree or mechanicalaxis alignment for the patient's knee undergoing the arthroplastyprocedure. Also, the overestimation process discussed above may beemployed for both the generation of jigs for total knee arthroplasty andpartial or uni-compartmental knee arthroplasty. Furthermore, while theoverestimation process is discussed in the context of knee arthroplasty,those skilled in the art will readily recognize that the concepts taughtherein may be employed for the production of jigs for other types ofjoint arthroplasty, including, for example, arthroplasty for hip, ankle,elbow, shoulder, wrist, toe joint, finger joint, vertebra-vertebrainterfaces, vertebra-pelvis interfaces, vertebra-skull interfaces, etc.Accordingly, the overestimation processes and resulting jigs disclosedherein should be considered as being for all types of arthroplastyprocedures.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An arthroplasty jig for assisting in theperformance of an arthroplasty procedure associated with a patientsurface including at least one of a bone surface and a cartilagesurface, the jig comprising: a first side; a second side generallyopposite the first side; and a mating surface in the first side andconfigured to matingly receive and contact at least a portion of thepatient surface, wherein the first side is configured to be orientedtowards the patient surface when the mating surface matingly receivesand contacts the patient surface, wherein the mating surface is definedaccording to the following process steps: a) identifying a contour lineassociated with the patient surface as represented in a medical image;b) using a computer processing device, evaluating via an algorithm theadequacy of the contour line for defining a portion of the matingsurface associated with the contour line; c) modifying the contour lineif the contour line is deemed inadequate; and d) employing the modifiedcontour line to define the portion of the mating surface associated withthe contour line.
 2. The arthroplasty jig of claim 1, wherein step c)includes adjusting a portion of the contour line to result in anadjusted contour line portion.
 3. The arthroplasty jig of claim 2,wherein step d) results in the defining of a surface of the first sidethat is associated with the adjusted contour line portion and does notcontact a corresponding patient surface when the mating surface matinglyreceives and contacts the patient surface.
 4. The arthroplasty jig ofclaim 1, wherein step c) includes: i) adjusting a portion of the contourline to result in an adjusted contour line portion; and ii) leavinganother portion of the contour line unadjusted to result in anunadjusted contour line portion.
 5. The arthroplasty jig of claim 4,wherein step d) results in the defining of: i) a surface of the firstside that is associated with the adjusted contour line portion and doesnot contact a corresponding patient surface when the mating surfacematingly receives and contacts the patient surface; and ii) a portion ofthe mating surface that is associated with the unadjusted contour lineportion.
 6. The arthroplasty jig of claim 1, wherein the adequacyevaluation of step b) includes comparing a first characteristic of thecontour line at a first location to a second characteristic of thecontour line at a second location.
 7. The arthroplasty jig of claim 1,wherein the adequacy evaluation of step b) includes comparing a firstcharacteristic of the contour line at a first location on the contourline to a second characteristic of another contour line at a secondlocation on the another contour line.
 8. The arthroplasty jig of claim1, wherein the adequacy evaluation of step b) includes comparing a firstcharacteristic of the contour line at a first location on the contourline to second and third characteristics of respective second and thirdcontour lines at respective locations on the second and third contourlines.
 9. The arthroplasty jig of claim 1, wherein the adequacyevaluation of step b) includes comparing an elevational change between afirst location on the contour line to a second location on anothercontour line.
 10. The arthroplasty jig of claim 1, further comprising acutting guide surface positioned and oriented relative to the matingsurface to result in a cut in the patient surface with a desiredposition and orientation.
 11. The arthroplasty jig of claim 10, whereinthe desired position and orientation allows an prosthetic implant torestore a patient's joint to a natural alignment.
 12. A femoralarthroplasty jig for assisting in the performance of a femoralarthroplasty procedure on a femoral arthroplasty target region of apatient's knee joint, the femoral arthroplasty target region comprisinga medial articular condyle comprising a medial articular condylesurface, a lateral articular condyle comprising a lateral articularcondyle surface, a femoral shaft, an articulars genu, and a capsularline, the jig comprising: a first side; a second side generally oppositethe first side; and a mating surface in the first side and configured tomatingly receive and contact certain surfaces of the femoralarthroplasty target region, the certain surfaces being limited to themedial articular condyle surface, the lateral articular condyle surface,and a generally planar area of an anterior side of the femoral shaft,wherein each of the certain surfaces are separated by regions ofnon-contact between the jig and the femoral arthroplasty target region,wherein the first side is configured to be oriented towards the femoralarthroplasty target region surface when the mating surface matinglyreceives and contacts the certain surfaces.
 13. The femoral arthroplastyjig of claim 12, further comprising a cutting guide surface positionedand oriented relative to the mating surface to result in a cut in thefemoral arthroplasty target region with a desired position andorientation.
 14. The femoral arthroplasty jig of claim 13, wherein thedesired position and orientation allows an prosthetic femoral implant torestore the patient's knee joint to a natural alignment.
 15. The femoralarthroplasty jig of claim 12, wherein the certain surfaces associatedwith the medial articular condyle surface are generally limited to ananterior and distal regions of the medial articular condyle.
 16. Thefemoral arthroplasty jig of claim 12, wherein the certain surfacesassociated with the lateral articular condyle surface are generallylimited to an anterior and distal regions of the lateral articularcondyle.
 17. The femoral arthroplasty jig of claim 12, wherein thecertain surfaces associated with the generally planar area of theanterior side of the femoral shaft are generally limited to beinggenerally distal of the articulars genu and generally proximal of thecapsular line.
 18. A tibial arthroplasty jig for assisting in theperformance of an tibial arthroplasty procedure on a tibial arthroplastytarget region of a patient's knee joint, the tibial arthroplasty targetregion comprising a medial articular plateau surface, a lateralarticular plateau surface, a tibial shaft, a tibial plateau edge, and atibial tuberosity, the jig comprising: a first side; a second sidegenerally opposite the first side; and a mating surface in the firstside and configured to matingly receive and contact certain surfaces ofthe tibial arthroplasty target region, the certain surfaces beinglimited to the medial articular plateau surface, the lateral articularplateau surface, and a generally planar area of an anterior side of thetibial shaft, wherein each of the certain surfaces are separated byregions of non-contact between the jig and the tibial arthroplastytarget region, wherein the first side is configured to be orientedtowards the tibial arthroplasty target region surface when the matingsurface matingly receives and contacts the certain surfaces.
 19. Thetibial arthroplasty jig of claim 18, further comprising a cutting guidesurface positioned and oriented relative to the mating surface to resultin a cut in the tibial arthroplasty target region with a desiredposition and orientation.
 20. The tibial arthroplasty jig of claim 19,wherein the desired position and orientation allows an prosthetic tibialimplant to restore the patient's knee joint to a natural alignment. 21.The tibial arthroplasty jig of claim 18, wherein the certain surfacesassociated with the generally planar area of the anterior side of thetibial shaft are generally limited to being generally distal of thetibial plateau edge and generally proximal of the tibial tuberosity.